This is correct. The epistle to the Hebrews was written TO WARN Hebrew Christians that they should not return to Moses and the Old Covenant, and anyone who did so would be trampling on the finished work of Christ and the meaning of the New Covenant. That is what "falling away" means in this context, and that meaning is supported in the epistle to the Galatians.No one that is saved can ever fall away because of sins of the flesh. Why? Because they believe, have faith in, trust in, have confidence in the fact that Jesus has already paid for all the sins of the world on the cross.
Judaizers who had believed on Christ were teaching that Christians must be Torah observant in order to be saved, and Paul had to refute that very strongly.
But after giving them the warnings, Paul had this to say: But, beloved, we are persuaded better things of you, and things that accompany salvation, though we thus speak. (Heb 6:9).