Why did he give up?
you have a better position after Ba3+ (up by about a pawn) but really he probably just got tired of chess or had to leave
I'm not sure why he resigned, but black does have a checkmate against white if white blunders if play continues
8... Ba3
9. Kb2?? 9... c6
then if black gets the queen on b6 after whites move(s) it is game over for white
I don't see why he resigned, he could have had to go to work and no time, or he could have seen a bad line like that and got scared
Your opponent robbed you of playing the 27 move mating combination on the board. Now we'll just have to see it in the footnotes to this game.