It should have been obvious to a person who trains dogs for a living that the dog in question was incredibly aroused by pigs and that it would attack them if he was allowed in proximity to them. The dog attacking the pig was completely foreseeable and he should be held accountable for engineering this situation.
No, Caesar Milan, the Dog Whisperer, did not commit an act of animal cruelty when a dog bit a pig during dog training. The dog was not expected to bite the pig. Furthermore, the Dog Whisperer did not encourage the dog to bite the pig. For his to be responsible, he needed to provide encouragement.
Caesar Milan should not be accountable for this attack, because dogs bite by instinct, only when they are hungry or feel threatened. He is training the dogs and teaches them to act on command of the owner, but he can not influence their instincts, because they are animals. He should be accountable for attacks only if he would give an order to attack.
While Caesar Milan has an obvious gift for training dogs, he cannot ultimately be responsible for how dogs behave - especially towards other animals. The dog may have been scared, or in the past, the dog behaved well in the company of other animals, so Milan figured the dog wouldn't bite the pig. Milan only has so much control over the dogs he trains because no one can counteract an animal's natural instincts at all times - no matter how gifted he is.