...is not Mittens.
This cat is the unnamed tomcat who plays the villain's familiar on Bolt's TV show. He is identified in the credits only as "Veteran Cat" (voiced by Diedrich Bader), which he's called to distinguish him from the new cat on the set, a Persian whom he invites to the roof of Bolt's trailer to taunt Bolt.
In fact, at that point in the movie, Mittens hasn't even shown up yet. Sooo... 's not Mittens, OK?