I talked to a friend who is a geologist, and he said seismic testing can trigger geologic movement, similar to what fracking does. So it's very possible that there was seismic testing going on (which is known to kill fish in the vicinity of the vessel doing the testing) and that the testing triggered an earthquake.
Apparently the USGS can tell a difference in their data when a seismic event is triggered by an explosion or other unnatural cause, and would not consider such an event as an earthquake. So, they may just being very precise in their wording by saying no earthquakes were recorded.
From what I've been able to tell, no permits have been issued for seismic testing to begin yet, so if someone's out there doing it, it is not allowed. I would certainly like to know more about this and hope somebody can get to the bottom of it.