Bottom line - the pilot in command is totally responsible for the safe operation of the flight. From that perspective, the responsibility lies with the guy at the controls. Having said that, there may well have been additional contributing factors.... The fortunate outcome was that nobody (as far as we know) was injured.

I can't recall ever seeing that maneuver at any T bird show that I have seen. They never seem (IMHO) to put themselves in high risk situations like that.. I'd be very interested to read what the accident investigators determine....