I had an 88 Chevy Pickup Truck that used the old style freon (R12). Man that stuff worked so good. In 100 degree heat that truck would stay nice and cold. It took over 20 years before the alternatives were competitive.
It's extremely good refrigerant. The biggest problem people have is that it ends up too cold and icing up the system.
It sounds dangerous, but it's really not. Propane is only flammable with the correct mixture of air. Otherwise you couldn't light it with a blow torch. Even if you have a leaky system it isn't going to leak fast enough to cause a issue. Also propane is significantly heavier then air so anything that leaks out is going to go to ground. And the amount of propane you use is not very significant.
Cars that end up having issues with propane are typically home built propane fuel conversions with no ventilation under the tanks or connections. The propane can then pool in the low places and build up enough to cause a explosion.
What you say makes good sense too since many RVs have propane refrigerators. I've long wondered how it works exactly. Probably time for a DuckDuckGo search.
And while its true that you need the right mixture of propane and air for it to ignite, with the right-mixture, you've got a fuel-air explosive formed right next to an ignition source (the car's engine and battery).
(That guy restores old refrigerators, so he probably knows a thing or two about refrigerant substitution...)