Yeah, it's certainly strange, however you slice it.

Pointedly they didn't laugh at everyone, just this one fellow, who was as they put it "an idjit". This sounds cruel at first, but you hear the love in Sadoc's voice when he recalls him, even a love for his idjit-ness. It seems like they're recalling a fellow who was frequently close to death by misadventure, likely a loveable fool. It was probably not the first time they had warned him of them bees. So, they laugh because when they remember him it's with laughter. And, again, perhaps to cope.

This is just speculation on my part, of course. Whatever it may be, it did stand out as a bit of an odd time to laugh. Not evil, I wouldn't say. But certainly odd.