are you talking about this one ?
https://www.helium.com/mineit's my first time hearing mining is limited to specific regions. according to their website, they only support america right now so i guess your friend is telling the truth. it's probably not because the hardware can't run in africa, but the company decide to limit the users near their area first for various reasons.
It's the hotspot infrastructure that lacking in those other regions so far but with time as people buy hotspot devices and set them up across the continents, there will be widespread coverage which will encourage more people to buy the devices.
As of now the US, Europe and some parts of China seem to have a high concentration of hotspots with Africa and South America yet to catch up but I do see some small hotspot dots in the continents as well according to
https://explorer.helium.comIt's just a matter of time.