They’d be better off courting the US for a trade pact. Africa isn’t going to be a mature business opportunity for UK firms for decades, if then.
Europeans have been working trade deals with Africans for generations. But the deals have been exploitative of accessing mineral, ore, oil, agricultural, fishery, and other natural resources. This is likely to remain the case, since Africans have never shown any ability to deliver added value needed for modern industrial development. Its fine for the UK, though, if they can make lucrative deals for the natural resources they can apply elsewhere to their factories in the developed world. Brexit had no role to play in any of this. Why the writer makes this connection is not clear.
PM Johnson has been taking lessons from the POTUS - good for him. I believe US/Brit trade talks will turn out great.