I do have an explanation on why that is the case though it does require covering a bit of history.
Contrary to what many people believe, terminology changes are not only caused by localizers feeling like changing things up but also done at the request of the original Japanese owners.
In the case of PSO2, Sega of Japan's own internal English glossary for PSO2 which you can sort of see in the English names listed during JP's end credits and the names used in the English soundtrack:
Any of you who played the SEA version might pick up on a few of these names in the album and credits listing. The SEA version was in fact based off of Sega of America's script for the original 2013 release which did use these terms:
However for the SEA release, Sega of Japan (for whatever reason) requested AsiaSoft do some small changes such as the infamous "Force => Wizard" and "Monomate => "Health Drink" (My guess is they wanted to make the game accessible as no Phantasy Star game had been "officially" released in South East Asia in the past) and there was also the complication that Sega of America's translation was never fully finished (they supposedly only got up to Episode 1's story) so some other portions were in fact translated by AsiaSoft.
So to go over it real quick:
SEGA of Japan Terms
- Forest = Greenscape
- Caves = Cauldron
- Tundra = White Summit
- Desert = Lost Sea
- Darker = D-arker
- Campship = Gateship
SEGA of America's Terms
- Matter Board = Paradigm Matrix
- Room = Quarters
- Exploration Quest = Patrol Quest
- Just Attack = Perfect Strike (Inconsistent with PSU yes... but consistent with Phantasy Star Portable 2's "Perfect Strike")
- Oodan = Woodan
SEGA of Japan/AsiaSoft Changes:
- Photon Arts = Photon Moves
- Techniques = Photon Magic
- Monomates = Health Drink
- Force = Wizard
- Braver = Samurai
Now what's this got to do with the NPC names? well basically... majority of character names are the result of that being Sega of Japan's "official" English spelling:
However it does appear that PSO2 NA did have "some" degree of control over some localization choices:
Pati and Tia's Sega of Japan English terms are "Patty" and "Tiea" (and "Patty" and "Tea" in the fan translation) despite the fact that officialy their names are meant to be a pun on "Patientia" (the language files even have a string entry for their two names combined in this manner... oddly). This name change was also one that was present in the SEA translation and which might have originally been done by Sega of America.
Sega of Japan does have an official English term for Falspawn... "D-arkers" yet for some reason the current localizers went with neither the original version or Sega of Japan's localized term.
Most of the area names use the original Japanese's versions displayed English name or make up their own.
Perhaps one I gotta give credit to the localizers for but which may be a bit difficult to explain so please accept this description from tvtropes.org:
In Japanese, each Dark Falz has both a kanji name and a katakana name. They are always referred to by their katakana name in voiced dialogue, but when referring to the specific Dark Falz the kanji name is used in text with the katakana pronunciation over it. The official English version consolidates the two by strapping the kanji's translation to the Falz's proper name as a title, i.e. "Elder the Gargantuan". (I might end up covering this as a separate topic with some examples of the Katakana / Kanji spelling for the Falzes)
So in terms of NPC names... it could really be one of the following: