Rumors can be fueled by certain aspects of the truth. When someone says "so-and-so are on heroin" would be a rumor, while the truth may be they are on some other kind of drug like uppers/downers or weed. People extrapolate the truth, and push the boundary enough to create a rumor. Something else would be if a celebrity and their significant other are not together at the red carpet. It could be they weren't feeling well, but the media will take the opportunity to say "trouble in paradise for x person."
I don't know if this even makes sense, but it makes sense in my head.
