I don't suppose you dismissed one of those "totally GDPR compliant" cookie bars right before that, did you? (You may have to think very hard; it's basically muscle memory for us these days...)

I've seen this trick in the wild. "No autoplay" means "no autoplay without some user interaction first". And clicking one of those "I accept" buttons is indistinguishable from clicking on any other random element to make it play a video. So they just made the "I accept" button play the video as well as dismiss whatever thing was probably covering up the website.

Some people are terrible.