Ocean water freezes at a lower temperature than freshwater. ... Fresh water freezes at 32 degrees Fahrenheit but seawater freezes at about 28.4 degrees Fahrenheit , because of the salt in it. When seawater freezes, however, the ice contains very little salt because only the water part freezes.
NOAA’s National Ocean Service
https://oceanservice.noaa.gov/facts/oceanfreeze.html
We don’t have a disagreement about this. Fresh water has a higher freezing point, 32 degrees, than Saltwater, 28.4. (I will try to remember this.)
It’s hard to draw conclusions about their survey because the information is incomplete. I am assuming they used hot fresh water to drill. If you hit the bottom of the shelf, all of a sudden all the water in the column (the water surrounding the drill)siphons down. Was there a standing column of water, or just enough to surround the Nozzle?