It's a bit confusing because the word ʿajamī simply means anything written in a non-Arabic language with Arabic script. Africa is certainly not the only place where that term has been used. It is also the case that Arabic script has been used to write West African languages for very many centuries. There is no way that guy can have grown up there and not know that so I don't understand what this article is up to. Possibly this is a separate adaptation using its own conventions for writing the local language. Probably just pop-sci sensationalism coupled with some rather severe mis-/non-understanding on the part of the article author.
I grew up in Northern New Mexico and now live in Canada, so know that "educational" efforts
which suppressed non-European languages and writing systems were too often imposed on
indigenous peoples in N. America. It would not surprise me to learn that some West African kids
were never exposed to "anything written in a non-Arabic language with Arabic script".