If you watch the movie you'll notice that right after it says based on true events it says that the tape was altered a great deal to pretty much make it scarier (meaning they added a lot that originally wasn't there).
The original movie filming before they edited it resemble that of ghost hunters on SciFi:
OH no, a floating speck, it could be a spirit!
Also, the blair witch is indeed a myth but whether or not it surfaced for the very reason of the movie holds a lot of speculation.
It's fluffy... a whole butt load of fluffy.