While there's definitely extreme ends of the scale between 'fan' and 'real person', there's a lot of space in between "guy who has encyclopedic knowledge of Star Trek" and "guy who thinks Star Wars and Star Trek are the same thing" and I've never seen a good dividing line, and whenever I've seen somebody try it ends up feeling less like a sound taxonomy and more "how much do I agree with this person".
Most people are fans, to some extent, and plenty of not chronically online people have brain-breakingly strange film opinions that you just don't see them posting about.