So, to answer the question: chuck roast is beef. Always has been, always will be. Pork has its own awesome roasts—shoulder, butt, loin—but it doesn’t do “chuck.” It’s like asking if a banana is a fruit or a vegetable. Technically it’s a berry, but you don’t put it in a salad. You just eat it and move on.
Now go forth and slow-cook that chuck roast. Invite friends over, pour some wine, and tell them the story about Pork Chuck Bob. They’ll laugh, they’ll nod, and they’ll never confuse beef and pork again. And if they do? Well, you’ll have a new family legend.