I have never heard of this rule. On the face of it, it just doesn't make sense. It is the ear's job - the human's - to retain the notes played over time, whether arpeggios or melody, or block chords in a progression. I don't get what this guy is saying. First off, minor 7ths don't resolve the way dominant 7ths do. In any case, "retaining" them at all times doesn't make sense.
See the thread here: "Chromaticism" where I explain the functions of 7th chords in detail.