Dunking is a pretty good representation of exploding to the rim, representing speed & leaping ability.
I guess you were talking about blowing by a defender, i.e. speed after the first step.
Kid has no problems blowing by his defender because of his quickness/dribbling/first step. He can get to the rim but has issues making the shot once he does.
This is an example of him being cautious about contact/possible injury issues. In high school he would blow by the defender and just dunk over whomever. But we're dealing with the big boys now. I still think he had injury issues the first year.
As we have seen in the past, the front office is not very forthcoming about injuries.