a pair of AirPods count as one device
you can only connect one regular bluetooth device to an Apple TV (or iPhone/iPad).
if you have beats or AirPods, you can connect 2 pairs, but both must be beats or AirPods.
Phone/iPad has done this for a version or two, tvOS has to be 14
AirPods aren't just BT 5, they do use it, but they have Apple's proprietary W series chip which allows more features than the regular BT spec, like auto swap and auto pairing using iCloud.