Ok, pitbulls are NOT ancestors of pigs. They snort because of the way there face and snout is structured. It's perfectly normal for pitbulls to snort. My pitbull sounds like a pig sometimes too. I find it adorable and it makes me laugh.
Some Pitbulls come from the same ancestor as and ancestor of pigs even though they are distantly apart they are some what similar. Maybe thats the reason or because he is sick and is growing faster and getting older faster than a regular dog causing reaction like snorting and coughing