I asked the same question on AOE history discord and thanks to one of their members for posting this. It is from “In Search of Sunjata, The Mande Oral Epic as History, Literature and Performance” on Google Books.
The history of Mandinka peoples of the Mali empire is mostly oral history - there is a lot less written history compared to Eurasia. So obviously we have no way for sure of knowing how much is true or not, but I think the fact that they pulled such an obscure reference and turned it into a unit shows that they did a fair bit of research.
The Musofadi gunner is an obvious reference though to the Dahomey Amazons which is quite anachronistic (they were from the 1800s!). But I guess it was a way for them to still get a hand cannonneer type unit while making it unique somehow.
