How in the world?

Have you read the article about the Czech guy who punked the Olympics by borrowing a Japanese team members number and skiing the 50k race? I'm not going to debate whether this was a hilarious prank or an insult to the olympics and the athletes who worked hard to get there. My question really is how this guy got through the security that people claimed was in place with someone else's number and did this race. And this is his second time doing a prank like this? I guess he knows how the system works at the Olympics.