Giles is a "preferred walk on," meaning he has the opportunity to earn a scholarship if everything goes as planned. I doubt if a promise was made by anyone, but since he was one of OU's top recruits at one time, I think his chances of earning a ship at some future date are better than most walk ons we see on our roster.
Preferred walk-on generally just means they're telling him he'll have a spot on the team.
I did that in baseball a hundred years ago. Coach said he promised to keep me in the program for a full year (if I followed the rules) and see how I developed.