A lot of aristocratic stately homes are XYZ House - there only being one privately owned palace in the UK. So I think it's just an attempt to make an office block sound way classier than it actually is.
As an example, here's a "House" not far from where I live:
As an example, here's a "House" not far from where I live:
https://en.wikipedia.org/wiki/Hopetoun_House