As others have explained, dressage is marked on individual movements. So even if you get a 0 on one movement - say a 20m canter circle and your horse just trots faster and does some kind of funky looking square shape, they are still perfectly able to get a 10 on the next movement if they do it perfectly.
Its great that Cinny went around the arena without bucking or giving any 'naughtiness' like the other horses, but a quiet, 'ok' test isn't what wins dressage. If you look at horses like Valegro and Totilas, they are very VERY hot headed horses. There's plenty of shots and videos floating around the internet of Valegro on his back legs in a full vertical rear.
As I think Allison and Maura have already covered, you need to read the course directives and description on each movement. Anybody can pull the horse around to the markers and do the movements with the horse in an inconsistent contact and on the forehand. Its the basic work that is the hard bit.