Ahh...the perfect martial artist. Haven't met him/her yet.
I don't want to speak for Mark Murray, but I don't think that's at all what he was saying.
For my money, assuming that someone is competent and determined (unless obvious signs point otherwise) is the safest way to go (definitely in a real altercation and for many situations in the dojo).
In any of those instances, I'd much rather expect competence and be proven wrong than the converse . . .