This isn't exactly an isolated incident, YouTube has lots of videos of autopilot steering wildly off course. The biggest problem is that Tesla allows turning on autopilot on roads that are not a highway and feature significant turns and hills obscuring "perfect lane vision", and the system is not prepared to handle that at all:
https://www.youtube.com/watch?v=ZBaolsFyD9I
https://www.youtube.com/watch?v=IOnuKrzCLYc