User blog comment:Zathronas/Analysis by an author: Volume 2 episode 11: No brakes/@comment-3387274-20141024221817

It was said back when aura was first revealed that animals could have it. Most likely Taiyang or any other part of the old guard thought the family dog might need protection.

At which point I would speculate that Oobleck sensed this, and used Zwei as a projectile in order to "borrow" that aura, in a sense, to add more force to his attack. Given that his conventional fireballs worked just as well though... it's possible he was just running on particularly warped trains of thought.