The article takes a while to get there, but it is focusing on a set of companies I hadn't heard of ("Transsion, Oppo, Vivo, and Lava") that buy components from last gen smartphones to make cheap devices to sell in the African and South(/east) Asian markets.
Presumably the supply of 5+ year old used phones that fully work is not enough to meet that demand, which is why these frankenstein Android companies exist.
You are underestimating these phones. Transsion is in the top 5 smartphone shippers worldwide together with Samsung, Apple, Oppo and Xiaomi. There is nothing Frankenstein about them: https://techeconomy.ng/transsion-ranks-in-top-5-worldwide-sm...