Link doesn't work, but found it. Man, that's savage. It's not a given that the bolter was at fault - limestone is constantly decaying and what was sound may have deteriorated. This has happened at UPT for example, where sound belays have had to be relocated over time as the rock has weathered nearby.
Practically, it's a tricky one - apart from looking for obvious cracks and loose blocks, how far do you go when you check before committing to a lower off? It's not like you're going to take a hammer with you to do a boom test.