Actually it applies to trad western astrology, too, especially the Hellenists, but you also find it in medieval astrology.
Anyway - he was confusing, wasn't he?
It's about a planet aspecting a sign that is in aspectual relationship to the sign that it's in.
E.g., Saturn is currently in Sag, so it opposes Gemini. If Gemini were your seventh house, you could expect some problems there.
He's also arguing theoretically. I've never seen anyone convincingly show what he's trying to get at. To wit: Saturn in Sag opposes Gemini. Even if it retrogrades, as long as it is in Sag, it still opposes Gemini. It wouldn't oppose Taurus unless and until it hit Scorpio in its retrogradation. The other side of the argument he seems to be making is that if Saturn is retrograde in Sag, it's really opposing Taurus. No, it's not.
He is correct in saying that the nodes do not cast aspects.