Revealing mistake: When Frank is knocked down with the tray, the arms of the person operating Johnny 5 are visible when the robot turns to run.
Continuity mistake: Just before we see Johnny fall off the bridge we see a shot of him speeding past some roadblocks. Look at the size of Johnny compared to the roadblocks. They are practically bigger then him. This was obviously a small replica robot filmed with the camera on the ground, to give off the impression it was the real thing. (00:20:45)
Continuity mistake: When Stephanie runs to the shelf to pick the second volume of the encyclopedia the amount of cats increases/decreases randomly between shots. Also, the amount of books and their position changes.
Other mistake: During the shot where Newton and Stephanie first argue ("did you say the the robot drove the truck?") in the background Number 1 is missing its treads, leaving the idler wheels and internal chassis of the robot's tread mechanism exposed. (00:45:05)
Answer: Astoria, Oregon is just across from Washington state on the Columbia River. The Highway 101 bridge connects Washington to Astoria, and it takes mere minutes to cross. Unlike Washington, Oregon has no state sales tax, so many Washingtonians who live near the border shop there, and their cars would be seen. Also, there are several vintage paddlewheel river boats belonging to a river cruise company based in Astoria. From a distance, they are a similar size, shape, and white color as a Puget Sound ferry. That is probably what you saw cruising on the Columbia River.
raywest ★