This is what I was confused about as well. In the example the meetup itself could be held as non-spontaneous (telepaths spare the price of the phone call), but deciding on the place will still be done on a whim, off the cuff, impromptu, not before, impulsively. Spontaneously? :)

(On an unrelated note, let me share my favorite Anglicism that I've heard in a movie: "gekidnapped")