The Chinese "dragon bones" have been proven to be dinosaur bones. They asked the people to go get some and they identified them as a known dinosaur.
LinkI see no reason a primitive civilization would not find dinosaur or prehistory large mammal bones. An earthquake or a landslide happens can unearth a large bone that must be explained somehow. And a number of mythic creatures have been explained this way.
LinkJust look at the
Dracorex skull. Even knowing it is a dinosaur, I can see how someone would think dragon with it. In fact that is how it got its name. Oddly enough Dracorex hogwartsia meaning "Dragon King of Hogwarts". Yea the Harry Potter Hobwarts.
While yes, it is not a 100% reason behind dragons around the world. It very well may be part of the reason. One of the great things about humans is our ability to make things up. It can be a great story or a new way to look at science. But we are thinkers and dreamers, and the view of a “dragon” may be from somewhere in our physique. And all we need is something unexplained to bring it out.