Could I have fixed this bug? Not even in my wildest dreams. Do I care how it was fixed? Oh no. No I don't. I just checked that the output of the LLM was reasonable.
The risk in this scenario is that after a few iterations of people applying AI-generated "black box" modifications, users start reporting that the ancient app is crashing on them now and then, and nobody has the first clue why, or how to fix it... and since the crash isn't readily reproducible, you can't even do a "git bisect" to figure out which commit introduced the regression. Now you're left with two unappetizing choices: either live with the instability forever, or roll back all of the "blind" commits to the last known-stable version and never touch the codebase again.