His statement indicates that he thought that “Loser owes the winner $x” betting was against the rules, but that “Loser owes charity $x”, which he offered, was not.
It turns out that neither was against the rules. So the warning is unreasonable and should be removed. And the right thing to do when you incorrectly punish someone is to apologize for your error. And, honestly, all the other moderators who think that the warning should stand should apologize too, for being ridiculous.