I don't know what people mean by this. He is a faster sprinter? He can jump higher and put in one-handed dunks?
Pemsl seems to have fantastic agility and athleticism around the basket - excellent positioning and body control when shooting. Cook definitely seems 'faster', but not as agile and sure with his shooting touch. Both are examples of athleticism, just different strengths and athletic in different ways.
If Cook learns some of Pemsl's skills in the post - positioning himself, faking out the defenders to sneak a shot in, looking to pass to a cutter as soon as the double-team comes, etc, then with Cook's better jumping ability, he may have a higher upside in the long run. But those aren't easy skills to teach...you have to practice that stuff until it becomes 2nd nature. Some kids 'have it'; others have to learn it.
That's kind of been the Achilles heel for many Iowa big men....they get down in the paint and they need to 'think' their moves out, rather than just react to where the defender is positioned and simply outmaneuver him to get off a shot, or look for a pass option. Woodbury was actually a pretty good passer in the paint; he just didn't have the footwork and skill to be a 1:1 scoring threat despite his typical height advantage.
Pemsl simply has a knack for feeling out where the defense is and being able to sneak shots by people without having to 'overthink' his moves. He is very very good using his pivot foot to get around people, and never looks 'hurried' or 'panicked' in the lane.