in reply to Advice on best practices
I think you have some valid concerns, especially if this is code you're working in tandem with.
I think you need to take the human approach here and just ask the person that wrote it or is maintaining it.
"Hey $author, I was taking a look at this code you wrote and I was curious why you did $thing this way?"
This way, it's not confrontational, and they don't really have an excuse to get defensive. You're there purely for educational purposes. I've found a lot of times people get kind of a sheepish look and go "yeaaaa it's really bad code, sorry, I was in an enormous rush etc." If they try to justify it with something stupid, well, you have your answer then.
Three thousand years of beautiful tradition, from Moses to Sandy Koufax, you're god damn right I'm living in the fucking past