Perhaps the pig was an service animal. They aren't all seeing eye dogs. Some animals alert their owners when they have (or are about to have) seizures, for example. These companion animals are legal to take into food/grocery establishments under the ADA, and often the restauranteur will know this if the person is a regular.http://www.epilepsy.com/epilepsy/rights_serviceanimals
There are a lot of other circumstances, but this is just one, as an example (I have temporal lobe epilepsy, so I know folks who use seizure service animals, although I do not).