Did he resign w/ his former team? If so, was he there 5+ seasons? That may be the 1st tie breaker, and if they offered the same max deal, perhaps he saved you time/effort by signing w/ his original team once they offered what others were putting up. That's about all I got, otherwise it does seem strange, all max contract guys w/ multiple offers have waited until the last day to sign.
One other thought, did you do something in budgeting that would have voided the deal somehow? Like tying up too much money in future seasons?