That's a hell of a lot of AC for that car cabin. Probably would have been cheaper to just fix the car's own AC than the cost of a generator and window AC unit. Maybe they just did it to prove it could be done?
A hundred dollar window unit, and a couple hundred dollar generator is going to be way less than fixing any ac problems that car might have. Not sure when you last priced mechanic work, but depending on the nature of their ac problems it could cost more than the value of the car to repair.
I have looked at car AC repair recently, and I could get a compressor for about $300 to fix the most major AC problem that cars commonly have.
Anybody who could install a generator and window AC unit into a car like that, in a fashion secure enough to drive with, should be able to install that AC compressor on the car themselves, which would remove the labor cost of paying a mechanic. An AC compressor likely only has a handful of bolts to remove on most cars, so you'd just need to jack it up and support it properly with jack stands, remove the compressor and replace it with a new one, then refill the refrigerant with one of those disposable kits that comes with a built-in pressure gauge.