It's very crude and not at all foolproof. For the lack of sophistication it's shockingly effective at highlighting a huge amount of assumptions we make about how software is / can be used.
If you tried ctrl+n (I think), you could advance to the next level, but only if you had beaten the current level or had the pass code for the level. In a bout of frustration, I rando-mashed the keyboard and advanced to the next level, and could then ctrl+n to the last level! I could reproduce the effect, but never worked out the actual combination that unlocked it. Good times :)
Fuzzing is a pretty popular testing technique for libraries, but GUI software has not seen the same attention.
Example of tools: https://www.fuzzingbook.org/html/GUIFuzzer.html
Something similar should be reasonably easy to build these days using AutoHotKey or the like. I bet it's been done.