I had it happen a couple times years ago in cars. 1 was Crower, the other a Crane. both broke at speed during a 1/4 mile pass, though. Just because it failed at idle doesn't mean the damage wasn't done at speed. (Still sounds like a bad piece to me).
Both cases the cam was sent back and free replacements were sent. In the case of the Crane, it was a small block chebbie and they replaced the damaged block as well! (This was back in the early 80's).
Hopefully no more damage was done to the engine, but I'd be ripping the whole thing down anyway to be sure.
Ray