It wasn't possible to stop at the speed the Waymo was moving at.

The Waymo didn't have the stop sign, the other driver did, at a three way intersection.

The other driver decided to suddenly enter the intersection, when the Waymo was like 5-10 meters away. This was after having stopped at the stop sign.

Either they weren't looking or intentionally trying to cause an accident. Swerving prevented the Waymo from crashing at 40 km/h into the driver's door.