A suggestion for you if you are participating in slot multiplier contest, try to find some slots where there is a chance to hit big multiplier in both normal spins and free spins.
Free spins are helpful in this way to help users are familiar with games and how games work in win and loss. Free spins are helpful for both professional and amateur players in many ways.
It is what it is, is all about luck and once you have luck on your side hitting a high multiplier could be achieved through any means including bug and system miscalculation although that doesn't come by as easily as thought.
Chance of hitting high multiplier and get big win on casino is very small because they have development and bug testing and fixing before launching the game to users. It can harm their business if many users hit it and win big so it is not common reason for a big win like this. I think casinos all set their max multiplier that users can win to put everything under their control.