The relationship is a little more complicated. A number of GAFCON-affiliated churches are still in the Anglican Communion, particularly (as you mention) in Africa. The Church of Nigeria, the Church of Uganda, the Anglican Church of Rwanda, and the Anglican Church of Kenya, for example, are all in the Anglican Communion.
In some other places (for example, the US, Brazil, and New Zealand), the GAFCON affiliates have broken away from the national Anglican church in their country and are thus no longer part of the Anglican Communion.
Sources: My own memory (I've been watching this closely), plus
Global Anglican Future Conference - Wikipedia and
Church of Nigeria - Wikipedia .