I have not read this in any of Utah State’s statement. They refer to his employment contract which would have pointed to the Employee’s Handbook. The only person citing it as evidence was Tom Mars in his response to the termination letter and he never claims in his text in the OP that Utah State referenced it in their letter. Mars is waging a public campaign with the intent to get a portion of the buyout via settlement.
If you can send me where Utah State uses the S/A handbook as justification I will gladly eat crow.