He may have been a subtle interpreter of Greek words.
Beyond that, however, his knowledge was insufficient for a thorough comprehension of Greek books, and especially of those written in the Hellenistic dialect.
In later life he became much better at Greek, and was at least able to check Latin translations competently against their Greek originals.
At this stage, Augustine listed in his Retractions
some the mistakes that he made in his early works through his ignorance of Greek.
The effect of his having had in his childhood a teacher of Greek who was cruel to his students far outlasted the seventy six years that Augustine spent on this earth.
Because Augustine was such an influence on the thought and scholarship of the Church in the West during the Middle Ages, his dislike of Greek unfortunately had lasting consequences.
His low motivation towards the Greek language and his recourse to Greek texts less frequently than would otherwise have been the case unduly influenced subsequent Christian authors of the West.
Because of Augustine, they disregarded the theological writings of the Greek-writing Church Fathers of the East more than would have happened otherwise.
One un-named teacher of Greek in the life of the young Augustine has much for which to answer, and Augustine should share some of the blame!
By way of an aside, it is interesting to note that Augustine was not an exception amongst the early Fathers of the Church for not knowing Hebrew.
Of the Greek Fathers only Origen, and of the Latin Fathers only Jerome knew anything of that language.
Augustine mentioned his lack of Hebrew more than once (Enarrationes in Psalm 86, 7 and De Doctrina Christiana 2, 22).
He recommended to others a knowledge of Hebrew, as well as of Greek, so as to avoid his own frustration with "the endless diversity within Latin translations [of the same work]." (De Doctrina Christiana 2, 16).