My late cat Raedthinn also knew how to open doors. He figured it out when I briefly lived in an apartment with door *handles*; he watched me use them, figured out what was going on and would reach up and pull the handle down to open the door. When we got back to door *knobs* he knew how they worked, but he could rarely get enough leverage on them to open doors. But “rarely” isn’t the same as “never.”
https://www.youtube.com/watch?v=qATc-ks78tU
If your cat is opening doors when you don’t want him or her to do so, don’t get mad at the cat. Cat’s doing what a cat’s *supposed* to do. Be mad at yourself for being outsmarted by a critter with a brain the size of a walnut.