GPS is actually far more accurate than that. There is deterministic jitter introduced to make civilian use cases precise to only a few meters, but military equipment has the algorithm to subtract that jitter and achieve precision measured in centimeters.

Anyway, that statement is highly misleading. They were comparing to previous inertial navigation systems, not GPS navigation.

Is that true globally? I seem to remember that some ocean areas wouldn't have as many satellites visible as e.g. polar orbits don't visit all of the globe.