When Matty T. came into form his senior year it was more like a 'he's arrived' then 'out of nowhere'. Expectations iirc were huge for him coming out of high school and it took some time for him to just play and react instead of worrying about the next step.
Of note, he was the one player that looked like they knew he was in a one and done situation that awful March day in 2015, his sophomore year.
I saw Ejim play on Fred's first team over Thanksgiving weekend and his athleticism stood out, was just raw is all. That said I wouldn't have predicted he turn into what he did.