This is a simplification of Unix history, but is in accordance with the fact that the first eager knon programmer) users of Unix were the people typing patents applications at Bell Labs.
See e.g. "unix, a history and a memoir" by Brian kernigan
I was thinking of it being sold to management as a typesetting system because Bell didn't do OS development. Unfortunately I don't have a reference immediately at hand.
That's funny. Not at all related but the Sidewinder heat-seeking missile got its budget from the fuses department, because it was "an intelligent fuse". (That's where it got its budget, but formally it was sold to management as "a rocket with fire control inside" because China Lake was allowed to work on rockets and fire control – they were expressly forbidden to work on guided missiles.)
