One thing that's always baffled me and that all cats seem to have in common is that if you sit down in front of a keyboard --- any keyboard:; computer, piano, whatever --- they have to jump up and walk across it.
When I was growing up, the cat would come and sit on the newspaper, if you spread it out on the table to read it. So maybe indeed something to do with a rival for attention.
When my mother was a child, her cat, Pippilew, used to sit on the (valve) radio when it was playing music in the morning, because it got warm. When my mother played the piano, the cat would come and sit on that too, hoping it would also get warm.
In your case I wonder if it’s possible the cat thinks you are having some kind of seizure, especially if you breathe heavily from the exertion. All he sees is apparently undirected, pointless physical exertion and heavy breathing!