I'd heard about that, yeah, that some people voted to leave as a joke more than anything else, and after the results were announced, they sat there all shocked and were like, "I didn't actually think it was going to happen!"
Apparently they forgot the fact that the vote counters aren't mind readers, and weren't sitting there going, "Oh, well, clearly this person didn't REALLY mean it when they voted to leave, they were just joking, so we'll put them with the 'remain' pile instead, 'cause that's what they actually meant." It kind of doesn't work that way.
If nothing else, this election was a good example of why people shouldn't act so flippant when putting down a vote.