The phrase "too simple"

I've seen three different peer reviewers criticize parts of scientific manuscripts as being "too simple", with little elaboration as to what changes are desired or what it means to be "too simple". For example, a reviewer told me that a method section of one of my papers "was too simple and not clear".

To my ear, "too simple" sounds like a mistake, but is it a feature of some dialect, such as Indian English? Or is it perhaps an established custom among non-native speakers, like beginning a question with "How to"? And what does "too simple" mean, anyway? Maybe "simplistic" is meant, but my best guess based on context is something more like "too short" or "insufficiently detailed".

I might be incorrect, but I think it means (depending on the context)that it needs more to it; more detail. But that is used when your professor/teacher annotates your essay and might tell you to make revisions.