Just to let everyone know: In practice, typical speed cubes (not Rubik's brand) are loose enough where the corner can accidentally be twisted[1], and if you get to the end with a corner twisted, you can untwist it legally. Well, unless you already stopped the timer like in that video. (Similarly, if the cube pieces fall off, you can put it back together. Also, if a few pieces are swapped in a way that makes it unsolvable you could take a few pieces apart and put it together again.) [2]

[1] https://www.youtube.com/watch?v=Vg23BI6sv1w

[2] https://www.worldcubeassociation.org/regulations/#article-5-...