Your statement could have been clearer . "They saw something that looked interesting on sonar, and they went to look for it." How about "on the way to investigate an interesting object on sonar, the ROV captured this frame in a different location.."
gl
Gary, The ROV wasn't always investigating sonar targets
If you read the dailies they also "mowed the lawn" on some days and spent time chasing after the stuck AUV a few times.
If the "17" on the debris image is the date then see partial quote from the dailes for that day:
"Dateline: Nikumaroro, 17 July 2012
"The AUV was hung up underwater for four hours last night. It freed itself and continued the mission but got stuck again as it was ascending for recovery at a depth of 722 meters (2,368 feet),
west of the island’s NW tip."
21:30Z (11:30 KOK)
"The rescue mission was successful – but it was a real cliff-hanger. Operating literally at the end of our tether,
we searched for over an hour in nightmare terrain: a vertical cliff face pockmarked with caves and covered with fern-like marine growth. We finally came across the AUV wedged cross-wise (parallel parked) in a narrow cave"