Its quite a confused map. It seems to mix up people groups and Kingdoms/Empires as though they're the same thing. So they show the Mali Empire, which was a united polity made up of various people groups such as the Mandinka and Bambara, but they've lumped all of the Akan together as one group, even though they were made up of very distinct and rivalrous Kingdoms such as the Ashanti Empire, the Dahomey, the Benin, and the Oyo. It shows the greatest extent of the groups it shows, even though that extent may only have been for a short period, and before and after, were split into other states.

It is also very selective about what groups and states it shows, as you can tell from the vast areas of uninhabited space. West Africa is overlayed with many colours. But Sub-Saharan Africa is almost entirely ignored. Some of the states and groups it ignores are the Kingdoms of Bunyoro and Buganda in present-day Uganda, the entirety of the Sub-Saharan Bantu tribes of Kimbu, Konongo, Nyamwezi, Sukuma, and Sumbwa, the Kingdom of Zimbabwe, Rozwi Empire, Mutapa Empire, Kingdom of Mapungubwe. These are just the ones I've found within a few minutes of searching.

I'd love to see a good map of pre-colonial Africa, with the Kingdoms and Empires properly mapped out. But unfortunately this isn't it.

It's certainly incomplete: off the top of my head I don't see Meroe in Ethiopia, the Geramantes in Libya, the various states around Lake Chad, and perhaps most egregiously the various Swahili city states the east coast. So your instinct that it looks a bit thin is dead on: this is a map attempting to compress what looks like over two thousand years of African history into a single map.

Beyond that the map is just kind of fishy. The Nok culture, for example, is essentially defined by a very unique class of portrait bust and perhaps associated iron smelting sites, but it is here given a well defined border and treated as a state. And the nature of the "Empire of Zimbabwe" is rather up for debate, with some seeing it as a collection of city states. So yes, I would say this map has a rather amateurish bent--it seems that somebody wanted to to create a unified map of African history, which is a noble goal but impossible.