"He used to not like beer."
Translation:Doedd e ddim yn hoffi cwrw.
I would think "Doedd e ddim yn hoffi cwrw." means "he did not like beer". Is this really the correct answer? In a previous instance, it mentioned "Doedd e ddim 'N ARFER ..."
This sentence uses the imperfect because it is about something that occurred more than once in the past.
The literal translation is 'He was not liking beer' which is not acceptable in English, so the nearest transposition is 'He used to not like beer'
The sentence 'doedd e ddim yn arfer hoffi cwrw' = 'he was not usually liking beer' can also be transposed as 'he used to not like beer'
It could also be transposed into 'he did not like beer' as you suggest, and this is one of the acceptable answers. However 'he did not like beer' could refer to one occasion of 'not liking beer' in which case it is:-
Hoffodd/Liciodd e ddim cwrw.