The issue is about someone maintaining the habit of downvoting without explaining why doing so. I think a downvote should always come along with a comment which explains why the downvote took place. Downvoting is not the same as not upvoting. E.g., when I am aware—I say "aware" because I've had moments where I had fallen prey to the Dunning-Kruger-effect...—that I don't grasp the gist of a contribution I neither upvote nor downvote it because I think judging about things which one does not sufficiently understand is not good practice.
Taking the fact that a contribution refers to OpTeX as a criterion per se for downvoting does not seem rational to me.
I find it difficult to comment on irrational behavior, especially irrational behavior of others.
Since voting behavior seems not always to be oriented to the matter at hand/sometimes seems not to be based on rationality/objectivity, but sometimes seems to be more a matter of the amygdala being triggered one way or the other—in the context of voting-behavior you also find keywords like "sympathy-likes" which means that with some people voting behavior also depends on the level of antipathy or sympathy they feel for the author, I form my opinion about the quality of a contribution not by looking at the voting results, but by reading it.
I feel that our interactions on this platform did not start all too well, which I am not innocent of, and which, by the way, I would like to change.
IIRC I did not downvote any of your contributions. IIRC I never saw a reason to do so, as they use to be focused on helping to solve problems and/or presenting facts accurately.
With the three examples you linked, I notice that downvotes were made, but there are no comments referring to the downvotes and explaining why they were made.
I think this is not good style on the part of those who made the downvotes.
I think that those who downvote should leave a comment as to why:
A downvote is a way of stating that you believe the downvoted statement deserves criticism. Part of freedom of speech is being allowed to express this in an acceptable way.
But one should justify this rationally. The practice of just conveying by anonymously clicking a button that there is someone who finds something worthy of criticism, but not what and why, does not necessarily contribute to an exchange of ideas/views that might lead to something constructive.
You have now composed an answer yourself, in which you wrote the following:
If this is LaTeX only site then rename it to latex.stackexchange.com and I will stop to use it. Or (better): try to educate users that there is no only LaTeX when TeX is used.
I assume that someone is using the downvote feature in a way that is not in the spirit of the site. I think this someone is an individual and does not represent the broad user community.
I don't object about notes regarding how to use the up- and downvote-feature in the spirit of the site.
But I don't know whether detecting and reaching (for educating) single users who don't use the up-/downvote-feature in the spirit of the site is easily possible. (Probably this is something which people can comment on who have more insight into the ways in which StackExchange is administered.) It should be considered whether confronting the broad user community with "educational measures" for behavior outgoing from one or two accounts corresponds to the principle of proportionality. (I say "accounts" instead of "users" because of the scenario of a single person maintaining several login-accounts.) I think the broad user community doesn't need "education".
Since the downvotes are not accompanied by comments that refer to them and provide reasoning as to why downvoting was done, everyone except the person(s) who downvoted can only speculate about the reasons for which these downvotes were made.
Perhaps an individual assumes that there is somehow a consensus that non-LaTeX answers are generally to be rejected.
Such an assumption seems audacious to me, to say the least. One should be careful about using assumptions about opinions of others as a means to an end or for justifying the belief that on can speak/act in behalf of everyone.
Answers are often united under one subject, which is not related to a specific format/flavor of TeX.
It may be that the text of a question mentions that the questioner is interested in LaTeX. But in most cases subject lines returned by the search engine do not reveal this.
This site addresses all variants/flavors of TeX. Therefore I think it is legitimate to think of answer seekers besides the questioner her-/himself and to give answers which refer to other formats/flavors of TeX but still address the matters raised in the subject line.
Besides, it doesn't hurt to be introduced to alternative tools/approaches. It even is often pointed out that it would be easier not to do a (sub-)task with whatsoever flavor of TeX at all but to do it with another program, and a corresponding workflow incorporating that other program is suggested without being taken umbrage at. So pointing to ways of approaching matters still with means related to TeX, even if probably not LaTeX, should not be a problem, too.
It often seems to me that a question is not only about how to implement the thing in LaTeX, but also about how to implement it at all. I.e., not only experience in implementing some algorithm in (La)TeX is missing, but the question is also about finding an algorithm at all that can be implemented efficiently for some TeX-engine. Therefore: If someone provides ideas by giving an answer that refers to OpTeX or some other format/flavor of TeX, that might inspire more experienced users to look at that code, to grasp the gist of the algorithm, and to re-implement one or the other of it in LaTeX. Et voila: A reference to LaTeX would be there even if the code provided in the answer is not based on LaTeX but is based on some other TeX-format.
I'd be sad if you were put off by a single user who might be using features of the site in ways in which they weren't meant to be used.
Even if someone should think that they can somehow speak for a general public through their downvote behavior, that doesn't mean that the general public agrees.