Wierd Resignation


I would prefer black's position at the end. Your opponent probably resigned because he couldn't finish the game not because he thought he was losing.
You're 7th move was not a mistake (although probably not the best move) since your opponent playing Bxc3 afterward is nothing to be afriad of because after taking back with the pawn you get a half open b-file and more possibilities for your bishop to get into play since is was blocked by your central pawn chain. Plus it gives you an extra pawn to undermine your opponents center with.

1.e3 I call that a mousetake (rather than a mistake.) What's wrong with 8.Ne5 (or 10.f4)? Ne5 wins a pawn outright, and f4 helps solidify the N at e5. If exf e.p., then Nxf3 is OK for White. I like 16.Ng3, intending Nh5, and if Bxg3, then fxg3 grabbing the f-file. As far as his resignation is concerned, I think it must have been some personal thing with him. I don't see a hidden mate-in-three or anything like that in your position.

I can't see any reason for black to resign this position: In fact, I'd prefer to be black in this situation.
A nitpicky aside, you said in your last comment that black has a passed pawn... S/he doesn't. A passed pawn has no pawns in front of or in files directly adjacent to it that block and/or capture it.