This is not the same as merely using cliches--a cliche may actually express exactly what you mean, even though you can instantly pick it out as cliche.
This is subtler. This is a language that sounds correct when you skim, but if you actually read it, falls apart into bits and phrases that don't work together and don't say what the author seems to want to say. It is as though, in an attempt to "sound like a writer", the author has abandoned their own words and phrases, and is attempting to cobble together the words and phrases of others, stitching them together in a Frankenstein's Monster with two left hands and poor fine-motor skills.
I'll give an example from my own life:
When I started middle school, the academic expectations shifted dramatically. In 6th grade, a "book report" was little more than a shoe-box diorama of a scene from the story. The summer before 7th grade, I had to write a real, multi-page book report, using actual words to explain things like what I liked about the book and why.
One term I ended up using in pretty much every middle school book report was "imagery." I claimed to like the particular book because I liked the author's use of "imagery," (which then gave me an opportunity to take up a few lines of text with a quote from the book, of course,) even though I actually didn't understand what this term means, nor did my examples reliably demonstrate the use of it. "Imagery" just happened to be an intelligent-sounding word which I interpreted as "the author uses words which make pictures in my head," which of course describes any book I like. What I could not do, what I perhaps did not have the words or training or skill to do, was to actually differentiate between and write coherently about the many different ways authors make pictures appear in my brain. Is the writing sparse, heavily slanted toward verbs and action? Or are there long, lyrical descriptions? Are the characters vibrant and fun, or are they meant to be more realistic? What of the pacing, action, or development of moral conflicts?
In the end, I did fine and made As, because cobbling together six (or was it twelve?) pages of something that sounds like English is generally good enough for school (especially given the high emphasis on regurgitating what you've learned.) Imitating others is a fine way to learn, one step on the road to truly absorbing the material and being able to truly use it. But ultimately, we do have to absorb, to make the language our own, to master its nuances and not just use words because they sound good in our heads, but because they actually say what we want them to say.