Basically, Tesla gets your information, then shops around with lenders that service your area, and bring the first positive result back to you. Being a ‘dealer’ Tesla is given slightly better rates than we as consumers get, but it’s still done through banks/credit unions. Rates are generated based on your credit score, and those rates are good for 30-60 days generally (varies by area). After that, the rates have to be recalculated.
Need anything more specific than that? I’m trying to be as general as possible here.