That video is outdated by at least 3 years now.
The video shows them using the old style thumb button return spring which had the small straight post that fit into the hole in the thumb button. Campy changed that post and made it a hook, so now you have to hook the little spring post into the hole in the thumb button before you install the thumb button return spring into the cavity and through the slot of the index gear.
Its makes this step a little (or a lot) harder than when that spring post was straight.
Its still a decent video to give someone a basic idea of whats involved.