to my knowledge, Bluetooth doesn’t work with airplane mode
The radio regulations were amended about 10 years ago to allow both Bluetooth and Wifi frequencies to be used on airplanes in flight. And so cell phone manufacturers have shifted what airplane mode actually means, even to the point of some phones not even turning off Wi-Fi when airplane mode is turned on. And regardless of defaults, both wireless protocols can be activated and deactivated independently of airplane mode on most phones now.
an airplane full of 100 people all on Bluetooth might create some noise issues that would hurt the performance
I don’t think so. Bluetooth is such a low bandwidth use that it can handle many simultaneous users. It’s supposed to be a low power transmission method, in which it bursts a signal only a tiny percentage of the time, so the odds of a collision for any given signal are low, plus the protocol is designed to be robust where it handles a decent amount of interference before encountering degraded performance.