You triangulate your Ngons separately in this lecture, while in the previous lecture we used the "triangulate" mod to do the same for the whole piece. This confuses me. Aren´t we doing the same thing again?
In a way, yes, except in this way we don't convert the quads to triangles. The only real advantage to that is it can make it a bit easier to unwrap, but you would be fine doing it either way!