Yep, and this is why central control, along with temperature sensors make a giant lot of sense to prevent such situation.

A simple thermostat is not enough, and even a PID one will not do the job if external thermal influx is not in the model.

I once worked on a HVAC controller for hotels in Singapore, and other commercial venues which helped the hotel operator to save on HVAC by packing visitors more closely depending on occupancy.

This avoid paradoxical situations of it being chilling cold in some suites with zero aircon use when it is +30 outside because of an unlucky combination of HVAC settings in neighbouring suites.

Doesn't all this imply there should be more focus on inter-floor and inter-room insulation, to effectively isolate floors/apartments/suites thermally from each other?

Quite possible parent was heating the loop water with their a/c which the North-facing residents extracted running their system in heat mode.

Which makes it all an incredibly inefficient system to move heat from the sun-facing side to the north side because you’re not allowed to prop open the damn doors.