I don't think anyone is saying anything happened overnight. We're talking a fifty-sixty year delay on the events mentioned above. But also, I would want to see some evidence that Africans on average weren't aware of the legacy of colonialism up until the 2010s, because that seems like an unreasonably low estimation of education on the continent.
Besides that, Russia and China also saw declines throughout the 2010s from peaks in 2009/2010. That would suggest to me that something in the 2010s made Africans on average less approving of the world's major powers in general