I am not sure that’s true, language can absolutely be misused, when an individual uses a word in a way nobody recognizes, it fails to function as language and is worth considering genuinely misused. It’s only when a “misuse” gains enough traction that people can effectively use it to communicate that it is an evolution rather than a misuse.
The point is that the language is about use, e.g. getting a concept across, and it can absolutely fail or be applied incorrectly.
Take for example if a variety of mugs are on a table and I wanted the red mug. If I said “pass me the green mug”, that would be a misuse of “green” as meaning red, and it would fail to communicate, as long as there are other mugs and my meaning cannot be inferred.
If there is clearly only one mug, a person might think I was mistaken or colorblind and still get my intended meaning, but it would still be considered a misuse of “green”.
If enough people used “green” to mean red, maybe because my family thought the mistake was funny and adopted “green” to mean red as an in-joke, it might grow out of being a misuse into a new meaning.
The same thing is happening when white children misuse AAVE and generate slang, “gyatt” for example meaning “god” as in “gyatt damn” becomes mistakenly applied to mean a butt because of misunderstanding about how gyatt was originally used. The misuse becomes new slang, but it could have easily remained an obscure and forgotten misuse if it didn’t catch-on with enough people such that it took on a new meaning.
I was imagining in my example that “green” might be adopted to mean red only in certain contexts, like used ironically or humorously to mean red, not in a way that erased or overrode the word’s general meaning as green. This is to match the symmetry of misused words like gyatt that continue to have their original meaning and use, but get warped into a new meaning through misuse and then adoption of that misuse in a certain context, such as among white children on Fortnite.
As opposed to a complete inversion or change of the meaning of the word such that “green” would no longer mean green anymore but only mean red (this of course could still happen, it just wasn’t the kind of case I was trying to illustrate).