We'll never know if it was deliberately thrown in there, which is obviously cruelty and not something I'd feature on here ever, but it's certainly possible as cats are very agile creatures and unlikely to fall in. However, the silly things are quite likely to sit on the very edge and look around at the world, unaware of the danger they're in.
I wouldn't post a video like that. If you're ever unsure, just let me see it privately first and I'll let you know.