One of the meanings of the preposition "de" before an infinitive verb is to tell the "usage" of something.
Creme de barbear = Shaving cream (the usage of the cream is to shave)
Quarto de dormir = Room for sleeping
Sala de estar = room for being, room to take your time, living room.
I'm pretty sure this was not deliberate but to do with the bot's inner workings. I've noticed that whenever there's a question that's completely irrelevant to the lesson there will be one word in that question that is in the lesson's word list.
Presumably the bot tries to find sentences with that word, but doesn't recognise whether they are relevant or not. At least that's my theory.