There’s no way the 12V battery is running the AC compressor. I suspect it literally just turns on the blowers to shift any standing hot air (i.e. ventilate, like opening the windows).
In my opinion an utterly useless function. I don’t understand why they didn’t include proper climate control remote engine start function. It was brilliant on my Jag XF (and even better on the Leaf of course as no engine running!)