1- Dinos themselves invented the so called "doggy style" when a Deinonychus male who fell on top of an offguarded female who was bent over checking its eggs resulting in unintended surprise buttsecks. A T-rex witnessed the whole incident but couldn’t make much of the details happening between the proportionally tiny creatures and took it as the newest trend in dino mating techniques. Later that night a T-rex carcus was found with its heart ripped out. It wasn’t clear why was the unsuspecting creature killed.
2- A Dino time travel to the future and witnessed the act of physical love between two dogs that inspired him to teach his own kind how to hump in this newly discovered position.
Away from all the time paradoxes, nobody can deny the fact that dinos used to hump using the exact same position and if we take a look at the historical timeline it is concluded that dinos did it first thus giving birth to the "Dinosauria mating" commonly known as the "dino style" position.
The phrase "Dragon Style" was created when a scholar couldn't remember the true expression and thus became widely popular among the online community in general specially internet trolls.
Great, These are dragons humping!