The 16ft difference is about half a millibar so insignificant given the QNH setting error.
This kind of accuracy is completely normal and I see it on every flight, over the past 7 years.
This is an IFR GPS but even modern cheap and dirty handhelds (Sirf-3 chip or later) get within 100ft. An EGNOS receiving unit (which currently has to be a handheld) like a Garmin 496 is routinely within 10ft.