Maybe, but it simply makes sense that it is.
+Undermine is directly mentioned in the story, connected to Khaz Algar, and was hinted at in Dragonflight.
+Undermine is a large enough location to fit as a patch zone and house a raid, and justifies the "Goblinraid" datamine.
+Undermine being patch content justifies the presence of Gazlowe and the Venture Co.
+Undermine is one of the most prominent underground locations in WoW lore.
+Undermine offers Horde content for 11.1, since so many Horde players feel that TWW is too Alliance centric in 11.0.
+Undermine in of itself connects to the theme of the expansion due to its underground location and it being a vast source of Azerite in BFA.
+Undermine makes sense as a city/hub with attractions and locations like the Brawler's Guild.
etc. etc. etc.
Versus Rootlands, which would simply be a 10.2 retread.