can someone please explain why my opponent resigned.

He lost the game already, or maybe he just had to leave? I did that once, I had to leave for a meeting while I was playing a chess game.

I'm more interested in how Stockfish leads you to a winning position from being down 2 pieces to be honest.
He does have an extra queen, though


He resigned on move 25.
Considering how STUPID he played, pushing pawns without a plan and weakening all his squares, he probably thought he looses the knight or something similar.
Seems the most logical answer

Based on a quick look, you are up the equivalent of two pawns, and it appears that you can quickly capture two more if you are so inclined (a4 & f6). Black may have felt that it was too debilitating to continue, i.e., perhaps he or she just wasn’t having fun and would rather take the loss without a fight than play on. Who knows?
I was playing this game against someone, when they resigned after my move. I couldn't figure out why, so I put the game in the Stock fish 8 analyzer, but even it said that I didn't have an immediate win or material atvantage. It said that I would have won on move 76 player perfect moves. Here is the game in my next post.