I don't know if I think it's funny, but I'm probably equally curious about two points. I do think that the journey is as important as the destination. I spoil things for myself all the time, mostly because I'm just always out of step with pop culture. It doesn't really impede my enjoyment of a well made book/game/film if I know some plot beats ahead of time. If you're just in it for the major plot twists, why not just read the wikipedia synopsis?

Also, there's the assumption that it was a real spoiler. It's not immediately verifiable. What if people were yelling "Snape kills Harry"? Why did the people in line assume the guy yelling into the night was being truthful, or that weirdly cropped images of pages weren't just photoshopped?