I had a game just now where after I tricked my opponent into losing a large part of an even larger group in end-game. He immediately passed, even though the rest of the group was unsettled (and honestly, without a mistake from him, it was going to live). So I asked him if we were considering that entire group dead, he didn’t respond, then I played the next play to continue finishing the game. He then said “bm dude” and resigned the game.
Am I missing something here? Was that really BM?