It must be contagious. Having never been asked before, I just spent a couple of weeks away and, like you, had three people on three different occasions ask me if my Yashica D TLR was a Hasselblad. After the third time, I actually got online to refresh my memory on exactly what a Hasselblad looks like. I can't see where the confusion comes in - the two cameras really only have two things in common... mostly black... a bit of chrome. So, yes, I think it's simply a case of a great many people only knowing one brand name of a camera larger than a 35mm SLR.
Well, there's also the waist-level finder (if you're using one on the Hassy). But you're right, the overall form factor is radically different. For all intents and purposes, the lens(es) on a TLR don't appreciably project beyond the front of the camera, and there's two of them.