The person you are giving as an example has more than 200 reputation on others SE sites, so she or he had a +100 association bonus when coming to TEX S.E. If you add his 17*10 reputations gained for Q&A on this site, +4 for accepting answers and 1 initial point, you have a total of 275 reputations before he offered those
From TeX S.E ...
Bounties are great! Showing appreciation to posts by bounties is great!
There are possible ways of bounty fraud, such as
shifting reputation to another account by bounties a lot
circular bounties (moving rep point to another account, and that account moves it back, costs zero but a benefit may be visibilty and so gained rep/badges)
What that user now does,...