I understand that although they are indexed at a the National Archives the records for the Royal Humane Society awards are held at the a British Library.
They suffered a cyber attack last year? Or perhaps even the year before, and are still not up and running as they were.
You might have to ask for a researcher to go and look at them on your behalf. As you have the certificate, it will have a date on it, so hopefully not too big a task for them to find.
Would “case notes” give much more information than the newspaper cutting? I don’t know.
Is the ship’s log available? the entry for the day in question might say something (or it might just say the sea was calm and they put a rowboat in to shore for water)