You ever been worried about a developer after reading the code?

I'm in a codebase right now that has all the signs of being really professionally done. Code structure is excellent, documentation, tests, etc. I'd assumed it was created by a team because it's a fairly big app, and while most of it is A+, some of it is really hacked: commented out code, bad formatting, dead-ends, no tests. It looks like the work of senior dev(s) and then edited by junior dev(s}. Or like an entirely new team was handed the codebase to support with no transition training.

I've since found out out that only one developer ever touched this code before it found its way to me. I'm finding myself wondering how they created such an image of beauty, only to start systematically destroying it from within. I seriously wonder if this guy had some kind of breakdown.

Mystery dev: I salute your hard work, and I hope you're all right out there.

UPDATE: The code was released and still in good shape. It had a clear changelog process, and multiple changes handled in the same professional manner. But at some point it just went off the rails. Like, a clear "before" and "after" status, not a slow degredation like happens as you get more frenzied approaching a deadline.