[2020] Misc. Question: What type of World Engine is guild wars 2 made with? (Mesh or Brush or "other" based)

Now, I know that the engine is in-house. But what I'm curious about is more the specifics of it. Is the engine/editor mesh based, like Unreal and UDK or like Source and Hammer? (Could it be somewhere inbetween like Radiant?)

I have asked multiple ANet Employee's ingame, but have either gotten "No idea, sorry" or conflicting answers of it being Mesh or Brush based. Hoping that maybe I can get an actual solid answer from the ANet employees that I know lurk this reddit (can't hide from me!)

(And for those who are like "this is silly", I'm just curious. I do level design as a hobby, so these things interest me. Much like people like baseball player stats, I like game editors/engines)

EDIT: So it's the general consensus also to figure out HOW you do this too, on top of what type of engine you use.