Not that I'd trust a self-driving car anyway, but if I were in his situation I would absolutely take the free ride there and back to get my stuff. It would be even more "massively wasting someone's time" to wait for them to do something else otherwise, which would entail a lot more risk.
100% agree, but, if that's the fix for the bug, I'd probably take an Uber next time. (I say this as someone with hundreds of Waymo rides)
Customer trust is a lot easier to lose than it is to gain. Moments of frustration are the perfect time to step up and prove to the customer that they can trust you to make things right.