That is absolutely correct. Writing isn't language, in fact. Language is instinctual and barring severe brain damage, everybody on planet Earth learns to communicate in at least once. (Sign languages are language. Indeed they're an extension of body language.)
Writing is an attempted encoding of language (and not a very good one, given how much is lost in written form vs. in-person communication!) and is a skill that takes a lot of time and effort to learn. Writing is not instinctual in the slightest.