Certainly you could take the view that you are and words do have different meanings dependant on the context in which they are used.
If the way it was used had been "I think it would be a dubious appointment" I could have accepted that but the actual context was that " he has a dubious history". That left me, and most of this board, with no doubts about its context.
Dubious can also mean not to be trusted, or not completely moral:
a dubious character.
There is no doubt in my mind as to which context it was used.
If Notts believes it was taken out of context then why not say so instead of trying to defend his action. Apologise and move on.