Why do I have to pair my devices again after changing the Bluetooth adapter? My computer runs Yosemite and has no working internal Bluetooth chip.

I therefore connect a Bluetooth adapter through USB.

Recently, this USB Bluetooth adapter broke. I bought a new one, and inserted that instead.

The interesting thing is that my previously paired devices still appear in a list, but they are not paired anymore. Instead, I get an option to pair them again.



My theory is that this happens because the USB Bluetooth adapter has some sort of ID number or something and that the devices are paired to that, not the computer itself. 

Is this true? If yes, what is this ID number called?
Every Bluetooth "thing", for lack of a better word, has a unique identifier. If it didn't, devices wouldn't be able to differentiate from one another. Walk down the street with AirPods here in a month or two and without a unique device identifier, you would get everybody else's music/conversations/whatever coming through your AirPods as you got within ~30 feet of them.

Your paired devices are still in that list because your computer remembers devices that were previously paired to it.