You're assuming too much. The lack of reaction was because 95% of the room didn't see him drop it or understand what fell. Even he stood there like nothing was

You're assuming too much. The lack of reaction was because 95% of the room didn't see him drop it or understand what fell. Even he stood there like nothing was going to happen. It could also have been a prank where he thought is was a fake but turned out to be a real grenade which would explain why he didn't even try to escape.