The 5 minute video is extremely misinformed if not outright wrong. There is no such thing as an "extended block" in the current form of Segwit[0].

I've linked to a better explanation down below. It does run 12 minutes but you only need to watch the first 3 minutes for a technical answer.

https://www.youtube.com/watch?v=DzBAG2Jp4bg

[0]:https://www.reddit.com/r/Bitcoin/comments/65uriv/a_simplifie...