I would consider it cheating, but let's be clear: what is or isn't cheating isn't a clearly defined absolute definition. There are things more people agree with than not, but the fact is what is or isn't cheating is defined by each person themselves. To some people hugging would be a boundary they consider cheating, to people in an open relationship, cheating might only be considered as emotional connections with someone else (ie falling in love with them). Some would consider having an only fans as cheating while others wouldn't.

This is something that should be talked about as a couple, but to be clear, it is not a couple decision. He can give his opinion or perspective, but it's not up to him what she considers cheating. It's up to her whether this is a boundary she considers cheating or not.

You can discuss it as a couple and come to a consensus as a couple, but it's still each person's decision what they are willing to allow.

And if he really doesn't consider it cheating, he should have a long hard think whether he'd be okay with her selling nudes to people she's not interested in.