"Choice of words" vs. "Unnatural usage"

I’d like to know how other tutors make a distinction between these labels when they correct writings.
I happen to use both as if they were synonyms. After all, if a student chooses a word that doesn’t fit in the context, this is an unnatural usage.

Choice of words implies usage that any native speaker would say fairly interchangeably. For example, I can choose to say that I have brown hair or that I am a brunette. That is only a matter of choice of words.

Unnatural usage implies usage that is, well, unnatural to a native speaker. I can’t think of an example since I’m really tired at the moment.

But basically word choice implies that they are correct in their words and unnatural usage implies a mistake.

Thanks for your feedback. However, if Choice of Words were what you say, I would never mark it as a mistake, because both “I have brown hair” and “I am a brunette” are correct.

Hi Mikebond,
I wonder the same question. I am often wondering what to choose.

As a rule of thumb, I use “Choice of Words” if it is a matter of diction (i.e. they write “It was super gross” in a more formal letter when they should write “It was quite unpleasant”) and “Unnatural usage” if it is a matter of incorrect usage (i.e. “I used a computer game” instead of “I played a computer game”).
I also would use “Choice of Words” in the situation that SolYViento describes and perhaps leave the Corrected version the same but write some alternatives in the Notes section for that correction.

I tend to mark it as “Unnatural usage” if none of the other categories fit. It can be a grammatically correct string of words used wrongly, a slightly wrong phrase (or something like much/a lot/many/very; muy/mucho; still/yet/already) and “Choice of words” if it’s a matter of “car” instead of “truck” and so on.