I was also very surprised to buy a car with cash, only to have a credit check required. It's a real thing. And according to this article, not required, but dealerships are confused by the language of the law and insist on running a credit check, anyway.
The dealership wanted to run a credit check if I were to pay with a personal check, but not if I paid with certified funds. I called my bank to have my debit card limit raised to $40,000 for 24 hours and paid for the car on my debit card with no credit check.
The system is rotten and (short of moving country) impossible to avoid.
There is no need to spread misinformation. While it is true that a hard inquiry will have a minor effect on your credit score (less than a 5 point hit), multiple hard credit inquiries from car dealerships or mortgage lenders within a period of 45 days only count as a single inquiry.
You're not at all disadvantaged by taking your business elsewhere, you're just making things up to furnish your dubious story.
That said, going in with a briefcase full of cash is going to cause a lot of other problems.