ok, there is actually bar Torah in Gemora:
Brochos 11 Shmuel to Rav’s son, looks like this is a reference to his father’s sayings.
Sukka 43 – same thing reference to father’s statement
Other references (only one in Gemora not to refer to someone’s actual father) seem to assume, like the posters here, that everyone know what this term means, even as it is pretty rare:
Gittin 62 has a Bar Torah Geneva (??) that Rashi explains as “ben Torah” who seems to like to argue – and has no (R) in front of his name.
More Nevuhim mentions that BT understands that even punishment from Hashem is not “bad”
Mishna Berurah uses the term in passing.