It turns out that many people received their invitations because of a system error.
A few weeks ago, players began to receive invitations to an event in London. Many people received confirmations that explicitly stated that they were one of five hundred people invited to the event.
The problem is that many people received invitations by mistake.
There were 500 people, and many more invitations. Some were completely unrelated to League of Legends, did not run any business for LoL, and yet they were invited.
Riot confirmed today that this is a mistake and the invitations will be withdrawn. Of course, some people should actually receive them, but they are not random people selected on the basis of statistics, a number of player entries or money spent.