It's definitely a local legend, and all the "evidence" is consistently unreliable witness testimony. That said, the doc does a pretty good job of setting up the non-supernatural/ cryptid possibilities.
Regionally, Mothman is a huge deal though. I don't know if I'd go so far as to say it's part of the local culture. (Though that's definitely true for Point Pleasant proper.) However, there certainly seemed to be a "mass hysteria" element that took over during the era of all the sightings. And the bridge collapse that ended the sightings was the worst in U.S. history up until recently.
