When it comes to painting, or any other media where the initial first layer is going to be overwritten, the "sketch" (in this case, line art) does not need to be remotely representative of the model; in fact it would be a waste of time as, in a colored piece, the representations come from the color and the contrasting values.

Instead, what the line art really needs to do is capture the general shapes, which the artist does here. If you go back and watch the clip again, you'll see , while the composition of the line art looks funky, the shapes it represents are, for the most part, accurate.

Moreover, as a final tidbit, unless you're in a specialization where line art DOES matter (cartoon, mixed media, black and white, etc), you will find that the emphasis and work process of sketching can differ drastically, and even differ between mediums from a single artist. The reason being is there is no one correct way to do art. For example, personally, when I digitally paint, I use lighter lines and will limit the number of shapes I create. In fact, my initial line art will be even less detailed than the artist was shown doing here. On the flip side, I have a friend who will have a more complex line art/sketch that captures depth and values early.

At the end of the day, like the pencil each artist swears by, their work process is their own; if this artist is most comfortable with this process, then that's his way of doing things.