Subset. Probably. Wrote a quick wiki page, since if otherwise it could be used as a subset of holding + headphones. So the character, similar to hands_on_headwear has to actually wear the headphones ether around the neck or head.
Would hands_on_headphones be used in the case of a character putting their hands on a headset or earphones? Neither of those tags currently implicate headphones (should they? or would that be too much noise? I hope we don't have to create another generic umbrella tag)