Technically not, perhaps, but I’d argue it functionally kind of is. Lots of people aren’t good at it, and it takes practice to get better at it.

Skill - an ability to do an activity or job well, especially because you have practised it

Seeing that almost nobody around me can take proper breaks because of all sorts of habitual factors it does seem like something you have to practise. Also, it’s an activity of actively not focusing on a stressor is still an activity. (Debatable in a tricky zen master way I know, but are you actually a tricky zen master?)

Seems like a skill to me.