How can I politely provide factual feedback without "attacking" the style of programming? ... the programmer is pretty young.
Given what you've shown, this seems to me to be as much a behavioral issue as it is a technical one. It looks like a situation where the older developer needs to sit the younger developer down and explain that behavior has consequences, and that coding (and commenting) practices are a behavior. This kind of talk is best done one-on-one, without managers present.
Unfortunately, that opportunity has been missed, and it's now "meeting with managers" time. Given that, I would focus on the technical aspects of the problems with the code and their likely downstream consquences. Avoid making it personal, even if baited.