Reebok deal doesn't start until summer, he's had those shorts in near every fight he's competed in. Reebok may have sponsored him since they signed him as an athlete recently, completely separate from the UFC deal, but it's doubtful they were made by Reebok, they're not part of the upcoming deal and if they were made by Reebok I imagine you'd be hard pressed to find the same pair regardless as none of the merchandising deals the UFC worked out would apply yet.
I assume Jones has his own deal with Reebok regarding the sales of his apparel since he's sponsored directly by them outside of Reebok/UFC partnership, but being as that was hashed out only a few weeks ago it's unlikely they would've been ready to get his gear together in time for the fight.
Additionally, the shorts had an EA UFC logo, which further suggests that the shorts aren't official Reebok gear, but just his normal fight shorts with sponsors as always.
