Why is this a blunder?

I thought this move (Knight takes pawn on b7) was good. I was confused why Aronian didn't play it until I turned on Stockfish, and it turns out Be2 at some point is a refutation. I have to admit, I'm impressed Aronian saw this. I would have blundered for sure, especially in a blitz game.

Doesnt Nb7 just lose to ...Nb7?

Nxb7 Nxb7, what next Bxb7 Kxb7? Lol

Maybe then Nc5+ stuff

Yep which isnt good for white.

But you lost a bishop for a pawn

BLITZ?! I noticed this right away

1. Bb7+ Nb7 2.Nb7 Kb7 Loses for white.

1. Nb7 Nb7 2.Bb7 Kb7 loses for white.

The point is Na5+ winning a pawn. Look deeper. but there is a better refutation

Just to clarify the line that wins a pawn is 1. Nxb7 Nxb7 Bxb7+ Kxb7 Na5+ Ka6 Bxb6 axb6 then Nxc4 winning a pawn.

But after Bxb6, there is a refutation. It's the only move for white. Can you spot it? (if Ka6)