If the grenades dropped on the floor when most people were sitting at a table the table may have obstructed shrapnel and prevented it from reaching any organs whose breach would result in immediate death (heart, brain, etc.). It would have to hit a major artery to kill near quickly on the lower body which isn’t a huge target.

Instead, it probably hit the legs and possibly some lower body organs, which can still be deadly but less immediate.

It’s insane that the guy who dropped them at his own feet survived though. Dude must be half shrapnel at that range.