It sounds more like situation where he was eating on zoom with mic on, while the second person just talked.
(I once got in a lot of trouble for having a bowl of cereal while I was a silent participant in a call with a client at a fintech company, so I understand that attitudes like yours are common.)
It's a matter of where is your attention. If you're eating you're not fully focused on the other participant you're interacting with and not being fully present for them is rude.
I'll often eat with other people, but I wouldn't take a sh*t with them.
Conversations on the can are less universally accepted. But do you ever see people go off-camera for a minute or ten? Some fraction of them must be listening from the loo.
I think the problem, as usual, is the power imbalance: they are eating and you are not, in addition to the fact that they have the money and you don't - so it becomes a bit too humiliating.