Its extremely uncharitable to assume he signed something. He even mentions in his article that other bands do require signing a license agreement to photograph but this band did not.
About how fair this arrangement is, you should remember that photographers with an accreditation do not pay the admission fee for the event and for a 3 days festival this is quite a hefty fee, I payed about 600 GBP for 3 tickets for Graspop festival.