The thing that I see that both pork and shellfish have in common is what can (pretty easily) happen upon ingestion when they aren't fully cooked. People consume undercooked red meat all the time - in fact it is considered a good attribute of the meal by some if the meat isn't fully cooked. But no one in their right mind would tell you to consume undercooked pork. The option for "medium" isn't even given for pork dishes. Same with shellfish.
I can far more easily imagine people of that time suffering the effects of eating raw or undercooked meats of those kinds (parasites, or bacteria-induced sickness incurring vomiting, etc.) feeling that THAT reaction was some kind of "Wrath of God" than I could imagine anyone thinking that God was punishing them by making it such that their pig couldn't follow along beside them as they walked a long trek, or that God was laying down the law by forcing them to keep traps in place over a long period to try and catch shellfish. I would think that nomadic living would just mean that you couldn't partake of certain things, but that wasn't the "fault" of anything in particular. However, these things are being attributed to God, as being items that will incur His wrath or make Him displeased - specifically.