This website claims that it's product can differentiate between these two fault currents. But I don't know what the difference is.
In a distributed DC system, a DC fault is consider either leakage or a short or missing conductors intended to be ground.
An AC fault has large capacitance and arcs with a small gap and sufficient voltage.
Their ground continuity tester uses AC 20Hz so as not to disturb the DC dynamics of system protection and variable constant current to isolate faults by the amplitude and phase of the voltage produced. Thus is an unintended conductor faults with a large capacitance it will have a surge discharge in current or drop in voltage.