More like, if someone steals $6 out of your pocket, would you trust them to keep walking behind you?
But, I don't think this is parallel to butt-dialing Uber.
Maybe if you had $6 hanging out of your back pocket, they flew out, someone picked them up, and when confronted said that they didn't do it.
Now, I don't know why uber didn't offer him the benefit of the doubt, but they were well within their rights not to refund. They did nothing unethical.