Unrelated modules often superficially look like each other at a point in time, I think that’s what the parent is referring to. An inexperienced developer will see this and think “I need to remove this duplication”. But then as the modules diverge from each other over time you end up with a giant complex interface that would be better off as 2 separate modules.

So deduplicating unnecessarily compresses the code without adding anything to code quality.