Just properly checked the head stem and it looks fine. First impressions were misleading, because someone hadn't done up the steering head bearing nuts correctly, and there was play in the headstock. Once everything was out and able to be examined properly, it's all ok. The bearings look very fresh.

In playing the 'what caused the crash' guessing game, I'm gonna suggest that the steering head bearings were replaced, but not adjusted correctly, which would've caused a thunking in the headstem while riding (it was massively noticeable just wheeling it into the workshop). This sort of problem led to a recent crash at the Creek by a mate on a Beemer, so it might be the cause here too.