While I have never been to Nigeria and can't vouch for their sorghum beers tasting like stout. They traditionally brewed various foodstuffs in iron pots with resulting richly tasting liquid. Because of the amount of iron absorbed into the slightly acid fermented product, the risks of iron overload are real, plus liver cancer.

I just wonder if this traditional habit explains their liking for Guinness?

https://www.reuters.com/article/us-nigeria-beer-idAFKBN2F710A

https://www.frontiersin.org/articles/10.3389/fsufs.2021.672410/full