that explains it, thanks!
I assume you have no plans to keep updating this game or anything, but if by any chance you do, I have two little suggestions:
make it a little more interactive. For now the game consists of dragging the mouse across the screen and being lucky. Maybe make it so that it's a bit more "work" to find the correct numbers? For example making the correct numbers slightly shake, become bigger or something similar, so you can recognize and "mark" them not by just being lucky, but by knowing that that is a correct number.
Also, maybe limit the maximum size of the square you use to mark the numbers, since you can just mark the entire screen and that makes the game a bit too easy.
I don't know anything about programming so I don't know if this is even possible inside PICO-8... but yeah, just wanted to give a layman's two cents :)