or the simplified both represent dragons, but not necessarily occidental ones. Since there are differences between Eastern and Western ideas of dragons (some relatively minor, some major) it is good to keep these separate.
would be a medieval European image of a dragon (LOTR, GoT). A wyvern is considered smaller, with two legs instead of four, without the intelligence or special properties normally reserved for dragons. A beastly lesser cousin of the dragon.
In Japan, the distinction between dragon and wyvern is likely unclear for most people, and the word wyvern is much lesser known. Likely for this reason the original naming chose 'dragon'. As wyvern is relatively better known among English speakers, however, the translation reflected this.