This article (and other similar ones) states:
In remarks at the White House on Thursday, US President Donald Trump said the drone had flown to within 1,000 metres of the USS Boxer and had ignored "multiple calls to stand down".
For airplanes, ICAO standardizes 121.5 MHz and 243.0 MHz (military) as common emergency frequencies that aircraft "should" monitor when possible. If approached by an unknown aircraft, this is the frequency I'll try to raise the crew on first.
How does this work for drones? Does the same standard apply? Is it reasonable that in this case the USS Boxer's crew could expect that the drone is monitoring 121.5 (or 243.0) and that its operators will be listening?