Dragon Fantasy is a two game series that started out with Dragon Fantasy Book 1 followed by Dragon Fantasy Book 2. Book 2 was updated to fix a lot of the issues with the game including some balancing ... they called this version Dragon Fantasy The Black Tome of Ice. Book 1 also got an update on many platforms but the Vita version was pushed back. This updated version is called The Volumes of Westeria. Book 1 didn't have as many issues as Book 2 did, so the update wasn't as important but now we finally get the Book 1 update (The Volumes of Westeria) on the Vita with this release.
So... there are two games... this is the remake of the first one. Though to be honest the first game was completely playable and awesome in it's Book 1 form. It's sad though the art for this doesn't reflect what version of the game it is.
To add to (but hopefully subtract from the) confusion, on PSN in the USA only Book 1 & 2 versions are available for the Vita. The Black Tome of Ice is only available on PS4 through PSN, though the Vita version got an EU PSN release. So currently this physical release is the only North American release for the first DF game on PS4... and the LRG versions for both TBTOI and TVOW are only available physically in North America for the Vita.
What I've opted to do to save my sanity is just keep the Book 1 & Book 2 digital versions on my vita, and bought TBTOI and TVOW versions digitally on my New 3DS. So I have both versions as Book 1 is completely fine to play as is without the update and I might prefer that version for nostalgic purposes.