Now, the dragons depicted in media are man made, so I see where you were coming from.
But the worldwide idea came from the real dragons that used to not be extinct.
Dinosaurs derives from dinosaurus, the Latinised version of the Greek deinos and sauros, which mean "terrible, terrifying" and "lizard" respectively. Dinosaurs are thus terrifying lizards.
Dragons are terrifying lizards. Ergo, dinosaurs are dragons.