Ah, that shouldn't have happened like it did.
If for some technical reason air conditioning isn't available on the ground, then company guidance is given for such occasions. Basically open the doors again.
Although the pilots should be thinking about pax comfort there are some low experience crews. Fantastic at flying but sometimes missing some other aspects of the job, like the pax consideration.
A message passed via the cabin crew should have prompted them to do something.
The captain can authorise non alcoholic drinks. End of.
Can I suggest if in the future it happens again then you ask the cabin crew to inform the flight deck before it gets too hot.