Primary school panic in the eyewitness testimony of the ninja, closed temporary school

An eyewitness testimony that "a ninja appeared" at an elementary school in the United States caused a panic, it seems that it has reached the temporary school closure.

I do not understand anything well, but what exactly is that?

Details are as follows.
Cbs3.com - Fake Ninja Causes N.J. School Lockdown

According to this article, it seems that temporary schools have been closed by receiving public eye schools in the American elementary school Barnegat, receiving information on sightings of "Ninja run through the forest behind the school".

The police confirmed that the "Ninja" was an instructor at a nearby junior high school camp and had a plastic sword wearing a black dress in order to enter the costume event.

It seems that the school was actually closed for about 30 minutes, but what is the image of "ninja" in foreign countries in the first place ...?