Can I please point out that the radiated heat from a fire will indeed kill the shit out of you even with your air-conditioner running. If you're within safe evacuation times, the car is a good bet, but if you're past the safe evacuation time you'd have better chances by staying put and making do with what you have.
Being trapped in a firestorm is a terrifying experience, it sounds like it's a damn good thing your uncle had the sense to find a safe place to take shelter!
He was based at the Fiskville training facility for a few years which would have been around that time and explain how he was at Macedon; prior to that he was a station chief so quite experienced.
The way he described the houses around them imploding and how the fire would rush out, take something and then suck back into itself sounded like a nightmare.
It was enough for him to have left the CFA a few years later.
https://www.cfa.vic.gov.au/plan-prepare/radiant-heat
(Sauce: I've been involved with volunteer bush firefighters)