I don't think he's insinuating that. To me, it sounds like he is stating that Tarm Sam developed a very specific method of hip movement and footwork, which other schools may have also adapted, but are still signature moves to Buk Sing.
There is nothing wrong with trading, exchanging, and absorbing techniques from other schools into your own methods. Sifus have been doing that forever. Only recently have people closed their doors and eyes to outside styles, thus halting their own evolution and growth.