Pitfall in the Nimzo-Indian

In the Nimzo-Indian defense (1. d4 Nf6 2. c4 e6 3. Nc3 Bb4), black intends to surrender the bishop pair with an eventual Bxc3, possibly inflicting white with doubled pawns. Deviating from this plan midway can be fatal, as one of my opponents found out. Coincidentally, this was both my best-rated win and shortest game ever:

Very good players. I've played hundreds or more in the nimzo and usually play A3 in the classical and have never seen black not take on C3.

Black could have gone c5 instead of 0-0

I dont see how a 2300+ player could make such a mistake/blunder. It appears he is resigning all of his games.... something smells bad here ......

Yeah, it's definitely suspicious, but I was willing to give him the benefit of the doubt. I thought he might have been overexhausted, made a stupid mistake, and then realized that now would be a good time to take a break from chess. After all, this game was the first one he folded, and the rest were folded several hours later on. I don't really see how this would fit the profile of a cheater...

On a more general note i have often seen good players arguing that giving up the bishop pair is not really forced in the nimzo, and that a good repertoire can be assembled with some GM-approved lines where black hardly ever takes on c3. That said the way your opponent choose to avoid the trade is definitely not appealing :)