> Dirt doesn't cause rust.

Dirt can contain salt, iron and other rust-promoting particles. And a caked layer of dirt can hold water against the metal part for extended periods of time.

> The two tow-trucks line is such a red-herring

That depends if the fault ultimately lied with the customer or Tesla. More broadly, it demonstrates the company's willingness to assist, to go beyond what most people would reasonably expect a company to do to help resolve a problem, even when it's possible the problem was caused by the customer.