I've tried turning it over without the spark plug in and it does spin faster, my assumption was that the starter was buggered so i'll probably order a new one and see if that helps
(the battery was low at this point but the engine doesnt spin much faster than it does in the video with a fully charged battery, and have tried with multiple different batteries) - in the video we have the battery connected directly to the starter so theres nothing safety wise stopping it...