Fractures to the back of his head might be consistent with slipping on the edge of the pool.
It is highly unlikely he would have two fractures and the other injuries by simply slipping and hitting the back of his head. "He has two huge skull fractures in the back of his head and he has internal bleeding in his brain and hematoma," Rucker's father Joseph told the Philadelphia station.
Nothing is impossible but I doubt this was caused by slipping on the pool deck.