I’m not sure I understand moving and closing questions stuff, but I’m wondering if it really makes sense to close questions like this as off-topic? I mean the user didn’t even ask the question on tex.stackechange and it isn’t his fault that someone else, inappropriately, moved the question here.
Closing a migrated question as off-topic 'rejects' the migration, sending any answers back to the 'parent' site and leaving it unlocked there. That is how the system is set up, and allows us to keep our site on topic. The suggestion made in the mod chat was to delete entirely from our site, but I am not sure that is useful.