By interference, I think of anything causing it to stray from the natural course of events. For Downfall to be the natural timeline, it implies that the hero was always destined to fail. The natural course of events would be that Link died.
We as the player, at some point bring about that interference, the moment that creates the CT and AT instead of the DT. We will never play as the Link that dies, because we changed something. Something that happened in the player's version of OoT is different than something that happened to the theoretical dead Link, allowing him to live and to create the other two timelines.
I don't know exactly what this point of interference was, but my running theory is that it was Zelda's prophetic vision. Had she not taken matters into her own hands, Link would have never opened the door of time, pulled the master sword, and allowed Ganondorf access to the Sacred Realm and Triforce in the first place. But because he lacked the Master Sword and Triforce of Courage, he inevitably lost that battle. More research is required before I can construct a full hypothesis.
Also, I hope that answered your question