If the car is titled in California, the transfer of the title is governed by California and also the state that the title is being transferred to.
"(a) No transfer of the title or any interest in or to a vehicle registered under this code shall pass, and any attempted transfer shall not be effective, until the parties thereto have fulfilled either of the following requirements . . "
California Code, Vehicle Code - VEH § 5600 | FindLaw
The buyer will have the consumer protections of his state and other rights under that state, but that is a different concept.