Mr. Andersson adopted his casting style because of shoulder pain. One good way to train against his style, which I refer to as 'pure' underhanding, is to duct tape your top hand elbow to your side, use a relaxed three-fingered ring grip on the upper hand, and use the bottom hand to 'stir the pot'.
Once you get it, it almost feels like cocking a Winchester 1894 with your bottom hand, and produces effortless, dartlike loops. Really fun.
what might be tough to catch on the video, as far as d-loop formation, is that this technique uses the bottom hand's motion to move the rod in such a way that the d-loop is formed and the anchor set. Henrik Mortensen's video's provide a near analogue, but Henrik's style is a little more loose, closer to modern scandi, but I've seen Goran also toss in some top hand arm, and even a little shoulder now and then.
Scandi casting becomes very individuated, very unique to each person who does it and what outfits they prefer, and the lines blur pretty fast under close examination.