How is it not? Certainly, one can't overgeneralize about such a huge continent. But it's neither South Africa, nor is it Somalia.
http://ffp.statesindex.org/rankings
On that list, Somalia is ranked 1, while Ghana and South Africa are 110 and 113 respectively. (For comparison, Finland is the champ at 178.) Certainly there are other ways to compare nations, and Ghana is not a perfect society. However, Ghana is exceptional among African nations, and it is a measure of the cluelessness of TFA that this fact isn't mentioned.
There are a lot of dense conurbations and they are fairly close to one another. That's obviously relevant for cell service.
Many parts of e.g. east and central Africa have lower-density settlement patterns that may be tougher to cover.