That’s not how I see it. Here’s how I interpret it.

Johnny practices his whole life to be the best he can. The devil shows up and challenges him, so he says it might be a mistake (probably knows the devil will cheat), but trusts his training and accepts. He plays his heart out and beats the devil at his own game, despite the devil trying to cheat. He wins the golden fiddle and, filled with confidence, says he’s up for another challenge. He knows he’s the best because he beat the cheating devil.

I don’t see it as talking about pride or gambling, but knowing your abilities and reaping the fruits of your labor. If it was about pride, he would’ve been caught by the devil.