Nb4? How do you find that square?

This game is over, I was black and when I put it through Stockfish it kept showing Nb4 as a move I should make. I can see the fork on c2, but I didn't think that it was much of a threat. Are there any other reasons to consider Nb4 at the following moves?

Nd3+ is also an annoying threat.

The b-file is kind of far to the side, so it's not a really natural move.  The c2 fork isn't too impressive to me either, but it does keep the queen tied down.  That's probably enough to make it worthwhile.  The knight is protected and can't be kicked, and you can always move it if it's more useful elsewhere (i.e., after the king moves).

nb4 is a good outpost that can go to other good squares

Hey, I just found something out you guys!!! You won't believe it and wish you had thought of it yourself. If N goes to b4 it can then go to c2 and d3, as well as a2!!!

I am a natural genius!!!

Genius!!