Taking a stab at it, I'd say maybe the football?
A college football if memory serves correct is smaller than the pro version. Also if memory serves correct, a pro football is also heavier weight (maybe from different materials or material cuts like thicker shell around air pocket.)
Then when you add in that the footballs are all new, unscuffed, and not worked in, and that might be another change he has to deal with. (unsure of the college football procedure for footballs in regards to this).
Overall maybe these changes are just enough to put him from kicker worthy of being drafted to being cut.
It may or may not be this guy's problem, but I just hadn't ever thought of the change in footballs before for punters and kickers. With the fairly recent change to brand new footballs all the time, it probably effects rookie punters/kickers now more than ever. But the exact measurement of how much it does effect is unclear.