This one [1] isn't very long, but I think it shows that the cat (Billi) does associate the buttons with a meaning.
The owner is playing with Billi with a toy on a string, then drops it on her back. She then quickly (within 10 seconds) presses "No", then "Back", to tell her owner to get the toy off of her back. If she was just pressing buttons to get a reaction, this would be no more likely than "Morning" "Love you", or "Want" "Hello", or any other arbitrary pair of buttons.
That is more compelling, but I'm still not convinced. Out of all the videos I've watched it's the only one that comes close. Smells like broken clock theory to me.
"No" is another higher-level abstract concept that I wouldn't expect anyone to master before more basic concepts. If the cat could say "ears, no" or "tummy, no" with similar confidence, then I would be convinced it understands combining the concept of "no" with another word. And those seem easy to test too. Cats don't like you messing with those areas.
The owner is playing with Billi with a toy on a string, then drops it on her back. She then quickly (within 10 seconds) presses "No", then "Back", to tell her owner to get the toy off of her back. If she was just pressing buttons to get a reaction, this would be no more likely than "Morning" "Love you", or "Want" "Hello", or any other arbitrary pair of buttons.
[1] https://www.youtube.com/watch?v=AYPFnDOPTQo