He’s caught up in the excitement of the moment, and, like a good sportsman, he’s acknowledging that Higgins fairly and magnificently won their bet. I think that, for Pickering in this moment, it’s not about Eliza. It’s about the wager. Pickering is a gracious loser.
He doesn't have to go that far. I agree that in this case Pickering goes somewhat out of character in order to make a dramatic point. To me this is a flaw, if a minor one. This only goes to prove that the greatest works of art are not perfect.
