From the article it seems like this ROV doesn't have sonar, and can only search visually at a short distance. They claim a distance of around 20 feet. I'm surprised they could find a debris field so fast with such a small range of observation.
Turns out that the debris field was only a few hundred meters from the bow of the Titanic which is approximately where they lost contact in the water column, so I suspect their search consisted of diving to the last known location of the Titan and then just going to the sea floor from there.
It appears to me that for all the rushing about (which was appropriate and neccessary if there were any surviors or surface debris to be found at all) the somewhat grim reality is:
1) hydrophones heard it implode at the same time it lost contact
2) it took until early 6/22 to get a deep-diving ROV on site
3) once the ROV got to the bottom, it swiftly found the debris from the implosion as expected
