Where in the heck did this idiot seller get the notion that they have the right to this information?
Tell your agent that the ONLY info the seller needs is the agent’s information (just in case anything is stolen or damaged while you’re looking at the house). If they have any *professional,* business-related questions, not related to your personal info, they can ask your agent.
Tell the other agent that you’ll report them for discrimination. They have no business asking about the “demographics” (or last names, IMHO) of people who just want to look at a house.