Searched the Gaga Reddit for Theory of Chaos and there's not much there other than this troll tweet with Gaga's face photoshopped onto the body of a drag queen named Frankie Wonga
https://www.reddit.com/r/LadyGaga/s/5jvGNFeH5g
Many times, it's a doddle.
You download a ticket from the SNCB website using your festival ticket number, then just use any ordinary train to Leuven or Aarschot (depending on which campsite you are in, I've only stayed in the Hive/Resort, so only ever done the Leuven route), then a free shuttle from the train station (follow the signs/crowds). They send out details much closer to the festival around May/June.