Thanks for the feedback JDplayer!
The main focus of the tutorial is identifying when it is 'check' and 'checkmate' as this is critical to understanding legal moves. This is why it is made clear when pieces cannot move (because it would place their own King in check) and also that moving a piece (that itself does not give check) can result in check which must be resolved immediately (a 'discovered' check).
As an experienced chess teacher, the thought of explaining all the rules of chess in one session (and using only one example game!) is quite a challenge. I hope you'll agree that by the end of the tutorial, beginners would have met all the learning objectives which are to learn how to:
1. use board coordinates
2. move each piece
3. 'castle'
4. promote a pawn (to a Queen)
5. check
6. checkmate!