"Quiet enjoyment" is a archaic legal term of art, arising (I believe) in law governing conveyances of real property. The Black's law dictionary on my desk defines "quiet" in this context as "Unmolested; tranquil; free from interference or disturbance." That is, it's not a condition imposed on the transferee ("if you do not enjoy the conveyed property quietly, I can make trouble for you").

The term causes enough confusion to be retired, but lawyers do love their stock phrases.