This news story has so little information it's hard to do much analysis. If there's a complaint filed in court, that would be much more detailed and useful.
However, If scare actors are trying to scare guest by lockers or other places where a guest would be intently focused on another activity and can get injured (e.g. bang their head, lose balance and fall, etc.), that's probably a bad policy. Despite the theme of the event, the park is still responsible for guest safety, and whatever policies are in place will get questioned up and down in a court case.
Wholly agree that it's the park's responsibility for guest safety.
However, if the guest had an extreme reaction to seeing a scare actor in costume in a scare zone that was clearly marked, especially when said actor was not actively attempting to scare the guest, I'm curious what a judge would rule since I'd think the employee acted within reason for v the initial interaction.
Obviously, more details are needed to figure out what actually happened, where, and by whom to figure out if the park had any role in it.
This could be akin to the McDonald's hot coffee lawsuit - on the surface it seems frivolous but in reality it only came about because the defendant (McDonald's) wouldn't assist with some medical costs when an elderly lady got burned by coffee that was being served many degrees hotter than anyone should reasonably expect. The plaintiff in that case allegedly didn't want to go for big numbers, more like $20-30k to pay doctors, but the defense kind of pushed her side to where it was warranted. However, it did force McDonald's to change their policies and procedures after the verdict.
I hope we don't see something like that where the park kind of brings it upon themselves and/or has to reduce HOS activities.