No no, not quite. The 120V detectors always have sounders built in because they are designed to be standalone. Sound in the bedroom is always required, but like Lambda said, just 15db above ambient, or 75db, whichever is louder is required at the pillow. If this comes from a smoke detector in the room or a horn/speaker outside the room it doesn’t really matter, but in a residential application its almost always built into the smoke head! The inspector was just confused because he’s never ran into a smoke without a sounder before, he’s probably used to the 120v variety being installed in homes.
Turn off your system and the 120v detectors should still operate as normal, they just won’t have a panel with a monitoring company monitoring them anymore, which is fine in most places.