so why would anyone bother with the hassle of 135?
Part 135 exists to make money flying the public around to negotiated destinations with negotiated prices. All of that is done prior to the flight and is well regulated.
In this case, you have a donor wooing a congresscritter by giving a gift; just as if you bought him dinner. Some sort of campaign finance or ethics violation was feared and so he reimbursed the gift.
I’m not saying the guy is clean, but I don’t think this is an FAR violation.