Pitts
I would think it safe to say that he understood a barrel roll - the pilot in question was a graduate of the Empire Test Pilots' School (ETPS), the very first Brit to fly the F117 Stealth Fighter (well before it was publically acknowledged), he flew Hunter, Hawk, Tornado, Jet Provost, Jaguar and a myriad of others including small aerobatic aircraft. As I understand it he was flying a display routine at low level in front of a crowd with tight display restrictions that he hadn't practiced very much.
Did he understand the barrel roll? - absolutely, as an ETPS graduate he could probably write you 10,000 words on the subject. Could he fly it safely? On a good day, yes, however he was probably having a bad day. He had been tasked at short notice to put something together - a pseudo role-demo come display without the normal full work up process. He paid for it with his life (and sadly someone else's).
Overall, Graham Wardell was a exceptionally skilled pilot who had a very bad day at the office...
I think that is why you have got BV's back up!
LJ