Amberdrake hadn't heard of a frag grenade, no, but the following explanation cleared that up. There were magical artifacts that had done similar damage in the War, albeit not by design.

He followed Cassian just enough to stay in conversation range, scritching Garth now instead of merely covering him. The little gold and black puffball had settled down in the dark of Drake's cupped palm, and was drowsing now, tucked up against Red. So cute.

"So you have a gun that fires something like that, and you use silver for the ammunition? I didn't realize you could change out what kind of metal went into a bullet," and he smiled, a bit, "though my understanding of them is rudimentary, at best."