meh fine, i'm wrong
in that case, I can only think of two explanations for the reason the Dragonmaw have that name:
either:
1) 'Dragon' here an translation of an Orcish word for a mythological creature of Orcish legend that was later equated with actual Azerothian Dragons after the Orcs first encountered them (like how the Chinese call Giraffes "Qilin" (c.f. Japanese "Kirin"); or
2) Dragons once existed on Draenor but had gone extinct before the 1st war. (this is not out of the question since Draenor and Azeroth share several genera of animals including:
Wolves,
Raptors,
Windserpents,
Owls,
Rock Flayers,
Spiders,
Wasps,
Moths
Chimeras,
Boars,
Dimetrodons,
Pterrodaxes
etc.