I don't know what he is betting ,but he clearly seems to have an edge over the 2-3 dominant sportsbook providers that are being used by most casino nowadays which is NOT illegal and the sportsbook has indeed the right to block him if they feel like it ,but they should be obligated to pay him the winnings atleast.
Why are you supposing so strongly that he is cheating in some way and "playing the victim"?
This is exactly my point here; If you want to block me. It's fair. I understand that. You have a business, and you decide who can enter in your business and who should be out. BUT, what you CANNOT DO, is STEAL the money of the person. Give the client the money and kick him out. This is ACT FAIR. I am not betting in fixing or something like this, so everything that is done is done under THEIR OWN RULES. This kind of action you NEVER see with regulated casinos. This way of proceed looks like MAFFIA.