A flesh and blood origin for part of the Bigfoot phenomenon need not be seen as precluding the possibility of a paranormal origin for part of the phenomenon, and vice versa.
Suppose, for the sake of argument, that human-appearing entities of paranormal origin exist--for example, ghosts, shadow people, Nordic extraterrestrials, or whatever. The existence of such entities obviously does not mean that flesh and blood humans do not exist. Likewise, the existence of flesh and blood humans does not immediately rule out the existence of ghosts, shadow people, etc.
The same logic holds for the Bigfoot phenomenon--the existence flesh and blood Bigfoot would not render the existence of paranormal Bigfoot impossible, and the existence of paranormal Bigfoot would not render the existence of flesh and blood Bigfoot impossible. Both could coexist, and the "true" Bigfoot phenomenon could result from a combination of both.
I would even add that, given the tendency of reported paranormal entities to superficially resemble some conventional organism or construct, perhaps it should even be seen as likely that, if paranormal entities exist, some of them might imitate flesh and blood Bigfoot.