Looking at the state of the players head I suspect it was more than a cup which caused that injury. As you say Hammers will get, ahem, hammered as it happened in the ground, can't see anything happening for what happened outside.
Looked like a cup from the footage, they even did a slow motion replay at one stage. Those cups had a handle on them so it could potentially have come from that, or the base. I mean it was only a flesh wound, but there was plenty of 'claret'