You are good at English for sure, at least in my evaluation (please take it as a compliment not as a criticism- I am not evaluating you as member of a examination board - who am I to? ).
From your anedocte I deduced you reached some conclusions (or you was obliged in a way to reach them). Firstly, any student at the very begginning is a follower of your master; thus, when we are toddlers we learn from our relations and parents and sometimes they teach things that we later notice are biased, improper or misperceived. Then, come teachers; politicians; physicians, lawyers and people from all walks of life; plenty of misleding for straightening up.
The truth is, we are born with a faculty of criticise, measure, weigh somebody else words and concepts.
One reading your piece of text would take sides and say: proverbs like this aren´t much used this days, yeah, but what´s the usage nowadays?
I answer: the use of words and expressions like 'da bomb' from wich 'bombar' in Portuguese derives. Also, in well known periodics we read 'planta' stand for 'fábrica' as in the English (here proper usage). True, in English 'plant' mean 'fábrica' and in other definition can be 'planta' a word that is with us for a very long time; but in Portuguese the former don´t suits well. And what about usage of "i" in small letter (lower case)?
But, hey dude; hold your horses! If your teacher wanted spare you from a overloading of tasks, informations and so on...this side of coin can´t be left out.
Because, for instance, when you are learning to drive, your driving instructor order you not pass through the yellow sign; don´t let you drive over 60 km or so (in Brazil) and oblige you to obey stop signals, even so you see that nobody´s coming (street is deserted).
Why is that, then?
´Cause he intends you learn the right way, after you get your drive licence is up to you.
So, some teachers go this way, step by step.
Mind you, if an instrutor begins a course lecturing your "followers" (student stand for follower in ancient Greek) on all words that spelled differently in Ame English and that Brit. one; and what about the difference position of prepositions in both languages!
This, reminded me about a native teacher that corrected a pupil of her/him on the use of word KID, he/her said "no way, KID is used only to animals, specially a young goat. The student had no choice but to accept, however it seemed fishy and later he clarified your doubt with another master.
I can´t infer what was your level at the time, so it´s impossible assess his/her goal.
Lastly, have a inquiring mind pays from the very beggining and ever will; we must learn from teachers, with teachers and in spite of them.
Remember, your apprenticeship is your sole responsibility, a very important thing to leave only in the hands of someone else.