A dragon is a "Ryu" (竜), a dinosaur is a "Kyoryu" (恐竜). The reason why it translates to "Dragon-Dragon fruit" is because it contains the character "Ryu" (竜), hence it's "Ryu-Ryu no mi" and every devil fruit names only uses 2 syllables eg Gomu-Gomu no mi, Mane-Mane no mi, etc
Besides, the two represents different ideas anyway. King being a "dragon" is about as relevant as Queen, Ulti, Page 1 and Sasaki being a dragon.
When people see a "Ryu-Ryu no mi", they see a 恐竜 (dinosaur).
When people see King, they see a "pteranodon"
When people see "Uo-uo no mi". they see a "龍" (dragon), which is synonymous to "竜".
The same "龍" that Ryuma slayed above the capital.
Therefore it doesn't matter the specification of the DF, because if Zoro was to slay King (the supposed dragon) above the capital, that "legend" to the people of Wano would be "slaying a dinosaur". Not "slaying a dragon" like Ryuma did.
Sit down, LePatrice:cheers: