Sold Car, Buyer Claims It Broke Down, Wants To Tow It Back To My House - Oklahoma

I sold a car in a private sale, which I understand is as-is, but the buyer is now claiming it blew a head gasket. He claims he saw evidence of a radiator leak, but there was no radiator leak. It had been checked out by a mechanic a day prior to the sale. The buyer test drove it, going up to highway speeds on a multiple-mile drive. There were no issues with the test drive. The buyer then left with the car. He reached out 3-4 hours later claiming to have a blown head gasket on the highway and demanding a refund. Here's the issue from my side - he is saying he will have the car towed to my house and be there to get his refund. Assuming this isn't a scam, the best case is the buyer (believing there was a radiator issue) drove it until it overheated so badly, it blew the head gasket. I do not believe that I owe the buyer any refund, but I also do not want him showing up with the now broken car and leave it for me to deal with. He is also threatening to take me to court over it. What are my options?