It is suggesting that there is an ideal cadence for their particular circumstances - strength, terrain, experience, fitness etc - but that it is useless to try to specify an "ideal" cadence in the abstract without knowing these things. So yes, make them aware that new cyclists tend to pedal slower than experienced ones, and that they should expect to operate at higher cadences as they get stronger, but don't tell them "you should be pedaling at c. 90rpm" because if they aren't comfortable doing it, trying to will probably do them more harm than good.