I'm a very open minded person, but I will admit legit proof or seeing something with my own eyes REALLY helps. This short clip is the end all be all footage of Bigfoot. But from documentaries and research I've seen from the 1970's up till now, this is my opinion.
Patterson was making a documentary ON BIGFOOT at the time of this footage. I believe for the documentary, he shot footage of a costumed preformer to put into the documentary, but after seeing the footage, and how realistic it looked as a genuine encounter and the subject being far enough away from the camera to look really good, he ditched the documentary all together and sold the "encounter" footage off as legitimate footage of Bigfoot being real. He needed money too, and got ALOT of name recognition as well.
Lastly, the thing that really gets overlooked is the breasts of the creature. In nature, most mammalian animals, and humans, female breasts are usually not fully covered in hair/fur. And the Bigfoot in the film has a pretty large rack, and they have a "stuffed" look to them, as they don't move or sag. Aside from that, it looks very authentic, thanks to the 16mm film which leads enough open to interpretation, especially when using modern technology to add to the paradolia.