I haven't read the novel or seen the comparatively recent film yet, but I saw both of the other film adaptations of the novel (The Last Man On Earth starring Vincent Price and The Omega Man starring Charlton Heston) and there may indeed be some parallels with how the eponymous man in either of those films views the strange, apparently subhuman creatures who roam the streets in the night. As other comments in this thread have noted, many indigenous people didn't recognize outsiders as quite human upon initial contact.
