That is wrong, I just generated 5 random letters in python and sent it to gpt-5 and it totally failed to answer properly, said "Got it, whats up :)" even though what I wrote isn't recognizable at all.

The "capability" you see is for the LLM to recognize its a human typed random string since human typed random strings are not very random. If you send it an actual random word then it typically fails.

I tried this four times, every time it recognized it as nonsense.