i dont think he should have resigned
A GM? I would be expected to resign, and I'm no GM, IM or FM (or NM...).
I bet I would get a lot of funy looks if I don't resign too...:) (not that it matters. against players stronger than 1800-9000+ (I'm at the ~2000 level), being a piece down for nothing (EVEN without 3 pawns down in addition AND being under attack. The piece is enough) is just hopeless).