If someone knows the Old Testament well, does this mean they know the Torah well?
If someone says that he knows the Old Testament well, he is a Christian. As such, he may know how to quote various verses but does not understand the Pesukim of the Torah. Those of us who learn Torah with the Medrash, Rashi, Ibn Ezra, Ramban, the Or HaChaim, Sipurno, etc. can be scholars in the Torah. The others cannot.