Sorry it was late and I should have been a clearer. I was asking for an opinion on the exercise. I've never seen anyone do it before but I googled and realise it's a thing that some do. As far as I'm concerned, the gym is a public place. I've never done it before but I've no qualms about recording something I found interesting /funny when it's legally allowed (obviously).
Now to read the rest of the responses
Edit: no I didn't approach him, he seemed to be in the zone per se.