Why would black resign in this situation? I was playing online with someone I do not know that is considerably better than me. I am still somewhat new and I can't figure out why they would resign after castling. What am I missing?

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1.e4 g6
2.Nf3 Bg7
3.d4 d6 
4.Nc3 a6 
5.Bf4 Nd7 
6.Bc4 e6 
7.O-O Ne7 
8.Bg5 h6 
9.Bxe7 Qxe7 
10.Qd3 b6
11.d5 e5 
12.g4 Nc5 
13.Qe3 Bxg4 
14.h3 Bxh3 
15.Rfe1 O-O 1-0
White gave up two pawns, the g-pawn and the h-pawn, without any compensation. Black's position is objectively winning. So my guess is that black had some non chess reason to resign the game. If this was a blitz game, then perhaps your opponent got a phone call or had to join the dinner table. From a chess point of view, black would have continued this game.