“True Christians had the Old Testament that the Lord used, the Jewish Canon,...”
Where in heaven’s name did you get this idea? Christ and the Apostles used the Septuagint which contains the Apocrypha. The so called “Jewish Canon” wasn’t put together until the Council of Jamnia in the late 1st century AD.
The Jews have always had the Torah and the Prophets. The books in dispute at the Council were minor books. When Christ said “It is written” he was definitely referring to Torah and the Prophets.
For lurkers, FTD subscribes to a 19th century extremist Lutheran Old Testament scholar who denies Septuagint.
FTD claims that LXX was retro-written by Greek Christians to make it "fit" the New Testament.
In other words, FTD says that Septuagint is, to put it simply, a fraud. You may want to take that in to consideration when discussing this with this individual.
Christ never quoted from any LXX or Apocyrpha.
The Council of Jamnia did not put any Canon together.
It only recognized what already existed as being the Jewish Canon.
Christ idenified the Canon in the Gospels, which was composed of the Books of Moses, the Prophets and the Writings, 22 Books, our present 39.