I think that is certainly a possibility, Hugo. The curved upper central is quite distinctive, although some older areoles appear only to have 1 central. Maybe the lower central appears later on as the plant matures a bit. It would be interesting to know the flowers.
Its an odd name though, as lepto means thin or slender, and caulis means body. so this is a thin or slender bodies Mammillaria. M. johnstonii is certainly not that, usually a smallish but usually subspherical plant. So where that name came from, I don't know.