This style comes from acoustic folk/blues artists such
as; Mississippi John Hurt,Big Bill Broonzy and Brownie McGhee and was also
used by 60's Folk players (check out early Bob Dylan for example)
The rhythmic use of the thumb underpins this style so it is worth spending a lot of time practicing just the thumb movement until you can do it without thinking about it.
The snip at the beginning of the video is to demonstrate what can be achieved using this rhythmic thumb technique. In essence it is based on the same basic technique as that shown in the rest of the video.
Learn the basics first and we'll get onto more complex rhythms later in the tutorial.