CG,
Ok, so I'm not in the RN, but I have got a brain and know how to use google, so how about this as an explanation....
Perhaps in the RN medical assistant is not considered a specialist submarine role, since medical assistants serve on surface ships and shore establishments. Prior to being posted to a submarine they undertake specialist courses, in radiation, atmosphere monitoring, etc. However, perhaps even those qualified for submarines are still seen as belonging to a core trade that is RN wide, but is undergoing shrinkage with the RN in general.
Quite possibly a weasel worded statement from MOD, in terms of no submariners being made redundant, but perhaps RN medical assistants knew their branch was in line for reduction - in which case would it have been fair that only those not qualified for submarines would be in the firing line for redundancy.....
Perhaps someone in the RN with more detailed knowledge would care to add some facts to the discussion to replace/supplement my conjecture!
As for being "sacked while at sea".... If it is anything like that RAF then compulsory redundees where given 12 months notice. Hopefully anyone on a sea going post spends a considerable portion of their life at sea, so it is hardly surprising that some people were at sea when the notification came through. One would hope they will not still be at sea in 6 months time.....