Just to play devil's advocate here - and by the way, I was there.........
The Rally had not finished for the day - I seem to remember the AIC notified the Rally TRA as being active until 2000hrs and the impromptu display certainly occurred way before this. There were other aircraft arriving and departing immediately before the Extras did their thing.
Did the AIC make allowance for arrivals such as that performed by the Extras? I can't remember reading it in there that you could carry out a display on arrival if you wished to.
Beig such highly experienced and skilled 'professional' aviators I'm sure the pilots involved had copies of the AIC with them as stated as a requirement in the AIC for any arrival at Kemble during the Rally - especially as the TRA was still in force at the time.
Oh, and what if a non-radio aircraft was arriving at the same time in total compliance with the AIC?
Just a thought or two.......