You can play with a 31/43/53 note keyboard yourself to see that you’re incorrect.

http://terpstrakeyboard.com/web-app/keys.htm

You can not differentiate two microtones playing together at the same time. Unfortunately, I could not test this with your link, because I could only play one after another.

You must not play an instrument because this is completely absurd.

I play the piano for a long time. And I have a clavichord that I tune myself and can tune microtonal to make such tests, which I do.

I can clearly hear different microtone combinations when playing multiple neighbors at the same time on the linked 53 note keyboard.

I'm sure at some point those tones will converge into a single note to human ears, but the fact that a 53-note keyboard exists shows that people can absolutely hear smaller divisions than just the 12 standard notes.