I don't think that's clear at all. This drone was in International waters, not Chinese waters, and it sounds like this device was not capturing any actionable intelligence but data on how sound travels through water.
Well, they needed both drones to locate the source of any sounds detected in the water. With only one drone, their tests can determine what sounds were made (and maybe some general vicinity), but not as accurately from where.
The Chinese already surprised a US carrier fleet by deploying a submarine fleet that "ambushed" a carrier when one of their subs surfaced in kill range to the carrier, undetected.
