Humans used this combination extensively for decades too. I'm no aware of any other simple way to grep both stdout and stderr from a process. (grep, or save to file, or pipe in any other way).
LLMs have neither muscles nor memories. They're token combinators based on statistical correlation, no more, no less.
That's not to say LLMs can't be useful when they string together tokens. Quite the contrary, in fact. But let's not pretend LLMs are something they're not.