Possibly they wanted it to stop near their destination somewhere and let them out, but instead it kept going. Therefore, they need to get out at the next place it happened to stop (which in this case was a stop light).

I have no experience with Waymo though, so I have no idea if this is the case, or if the car was repositioning to find a better place to let the rider out, or something else entirely.

Some of us like to jump out of moving vehicles and do a cool roll or flip like in an action movie! This is yet another use case the Silicon Valley technocrats didn't consider...