Without reading the case as well, the arguments in your linked article are that the person attending was there for fright, and the analogy given is similar to someone suffering a baseball related injury at a baseball game. Similarly, ski resorts are not liable for ski related injuries unless the resort acted negligently.
As a general theme park fan, I have my problems with Six Flags operations and generally believe they operate rides negligently, maintain the park negligently, and cut costs where they really should not. That being said, having been to many of their fright fest attractions, the staff are very cautious of crossing any unsafe lines. It makes their Halloween attractions relatively tame compared to the competition. Specifically to this case, they explicitly make it clear that you can’t touch the scare actors and they can’t touch you. So choosing to run when someone gets close is a personal decision, coupled with the point of attending an explicit fright attraction, the ruling makes perfect sense to me.