It was probably found by Rhombus while seeking a main base of operation for the Texas expedition against Attis and his super mutants. The place appears to be a Vault-Tec facility, probably dedicated to the Secret Vault project, a vault prototype. Some valuable technology and inventory, like working computers, laser grids, functional steam pipes, radioactive drums, gun bots and holographic devices were found there and used for training new initiates.
In the game, Nadia completes this course, guided by a Paladin hologram, while various people in Vault uniforms watch her progress. These people are probably the Brotherhood of Steel members who simply used the uniform found in this location.