Starfleet Officer, Starfleet is made up of Commissioned and Non-Commissioned Officers. In some of the shows, mainly Voyager and Enterprise, they labelled the generic characters as Crewmen (even when some of them have rank)
Its the military today who get hung up between Officer and NCO(fficer) ranks and who gets called an Officer.
It's seems to be exactly this. Although they are similar, they're ultimately different services with different terms and values.