I think you are reading too much into this - they were literally not casualties but interned. So their names were not published on any casualty list. I assume they were missing in action in Norway and it took time until their MIA status changed to interned. In the time it took them to get to Sweden and the their names to be sent back to UK by the Red Cross they would be listed as MIA as there was no confirmation of their deaths.
Alan I think I understand the point you making, but as Graham points out, the bit I have highlighted is not correct. Their names were on a casualty list, because that's what the document where they are listed was called, as you can see from the heading from the previous page, shown below.
All occurrences of this type - deaths, injuries, capture, internment, missing etc - were (and still are) all termed 'casualties' in military parlance, based on a different meaning of casual, namely irregular, not permanent, as in casual labour.
However your wider point is correct; these men were not injured and it wasn't in the public interest for their whereabouts to be released to the press in the same way that lists of men known to have been killed, injured or made prisoners of war were released for publication.
Today the MOD has a Joint Service Publication - JSP 751 - which is the complete manual for how to handle all types of casualties. It includes a section on dealing with the media, part of which says "The names of other [that is, those not listed as killed] casualties will not be released, other than in exceptional circumstances, and must only be carried out with the consent of the casualty or, if they cannot be consulted, their [emergency contact]".
