I don’t believe that is real prank stuff. I mean, the reactions would be much more extreme if someone really did think they had just seen a giant man-eating spider/dog.
Still made me laugh but not convinced.
I’m not sure that people actually think they’ve just seen a giant spider, just something quite large, that they can’t identify and so the flight reaction kicks in. You don’t really think you just run, thinking “WTF was that?” after you’re out of the ‘danger’ zone. It’s also always in a quiet area, if you saw it running along the street in broad daylight, you’d probably rationalise a lot more.
In America someone would have probably shot it.