“while another French-flagged ship was no longer involved in the rescue.”
Sounds like the French-flagged ship gave up already.
Or had fuel vs distance issues. Really if the ship can't cut through the ice and doesn't have a Helo on-board, then it is another potential liability in an already bad situation. The Russian flagged ships Captain may have released the French ship from the rescue or Australian officals may have.
They probably got the report on the ice being over 2m thick, when most icebreakers won’t do much over a meter.