I agree that this just looks like a guy trying to re-home a clearly unwanted animal. It is far better for him to be able to post on craigslist so there is a chance of the piggy finding a new home with someone who cares and knows what they're doing.
If you report him, given how much he seems to care, he might just throw the animal away outside or give it to someone to feed to their pet to get rid of him. I can't imagine that is a desirable outcome.
Craigslist may have many unpleasant ads, but its not craigslist itself that creates these people. It may be a gathering ground for these people given the ease of posting, but on the plus side it provides a medium for people who might otherwise be too lazy (or embarrassed to ask people in person) to find a home for their unwanted animal. If they didn't have this I imagine many more people would just get rid of or destroy an unwanted animal to avoid the trouble of asking around and trying to find a home themselves. This way a caring individual, from a ways away, can find them.