You really don't know the arrangement Panda has with his supplier though. In one scenario(and this is what any smart businessman would push for), they worked it out so the supplier counts DO's volume towards pandas, leveraging a better rate for Panda, which would yield him better margins. He is established, has the first mover advantage, and will always do more volume, so this is beneficial. The benefit outweighs the risk of adding another competitor.
Not to mention, If he didn't introduce dragon, he would have just went elsewhere. Supplier loses the business in that scenario, and Panda loses potential supplier discounts.
Really been enjoying watching this whole Panda/MK/DO thing unfold. Who needs TV when you have this sort of suspense.