Nick Saban said he could play Safety I. The NFL. Ran a 4.6/40. Yikes. Yeah he might be better at Safety.
He's not a track star, but that really might not matter. Also, some players play a LOT faster than their 40 times. Tank Dell only ran a 4.49 but that guy is lightning quick. Quickness and change of direction speed can matter more than straight line speed.