If he lied about it, he might be subject to legal challenges from his investors. It also has been done before by other companies. So it's probably true.

I read the “it” in “has been done before” as “Elon lying” and “other companies” as “Elon’s other companies”

He is willing to pay the price of legal challenges for the benefits of public attention, and on a less rational level, he simply doesn't care and has not ever faced real consequences for it.

“Elon would never lie!”

Celebrate With Us: Elon Has Been Promising Self-Driving Cars For Ten Years

We take a look back at a decade full of headlines that did not contain those four little words Elon longs to hear: "Teslas Are Self-Driving"