Hello Shikaio, great to see you on the forums and welcome back!
Your guess is exactly correct yes, VoxElyria allows the developers to work on a number of mechanics which are independent of the Unreal client like contracts, NPC interaction, etc. A lot of the work in VoxElyria can be done without having to duplicate for the later client. You can read a bit more in this DJ from the past (Note back then VoxElyria was named ElyriaMUD as it was planned to be more of a text-based client),
https://chroniclesofelyria.com/blog/17384/DJ-19-PreAlpha-Experiences