There is a scientific basis in cleaning, drying (reduced weight of moisture, particulates etc), rubbing and warming up the ball. It will enhanced the trajectory and flight of the ball.
By using a 'towel' Delap does affect the ball. These are the esoteric tools of a thrower or a ball striker in most sports. Any slight advantage adds up. In Delap's case;
1. Delap's technical ability acquired through background as a javelin thrower.
2. Width of the field and 'towel' provisioning
3. Throwing is more pinpoint accurate than kicking, especially when target has prior experience with the thrower (who can identified opponents weak spots etc.)
So all these tiny advantages adds up eh?
My suggestion nice time either don't give him a towel or provide him with a wet or greasy towel.