I have noticed that during a conversation, someone will say the odd word in the French way. For instance, The Dowager might say 'they were preoccupe, instead of preoccupied' Was this something the nobility did in those days?
Very common custom among the aristocracy of Europe from at least 18th century forwards. They were brought up to speak at least some French, and to read French novels (at least to some extent), and some of those phrases just got to be common catch phrases,
Very similar to how Europeans today mix English expressions into their speech.
Its also fairly common even now for an English person to use the odd French phrase, decidedly de trop, par example. Faux pas. Excusez moi, that kind of thing. Un petit peu. Perhaps it's a hangover from 1066?