Well, a lot of what they call "dragons" here are just so very different from the ones back home. Not that ponies know all that much about dragons to begin with...

[A point driven home so hard to her when her assistant had pleaded with her to tell him more about his species.]

For all we know, there could be all sorts of dragons out there. The dragons we're familiar with could be their equivalent of pegasi, and there could be earth dragons and magic using dragons that nopony's ever seen.

... I don't think it's likely, mind you, but it's possible.