That's nonsense - people want to know the reason. If it's a shortage of train crew, it's a shortage of train crew, whatever the background reason may be. It's nothing to do with a train fault. The reason comes down to the company running the trains, not its staff members and any "threat" needs to be dealt with robustly through the proper channels.
"Resource availability" and "shortage of train crew" are essentially the same thing when you think about it - except one is clear english and the other is actually rather vague. I am surprised TfW got that agreed, although certain TOCs have slightly different ways of explaining the same thing. For the record I also don't like "operational incident", but sometimes there is no easy way to explain staff error without getting into the minutiae of the railway (SPADs, wrong routing, wrong side door release, etc.).