Nevertheless, he is still being held and will be questioned again today, police said.
The terror threat in Rotterdam on Wednesday night was unconnected to the attacks in Spain earlier this month, despite the Spanish link, sources have told international news agencies AP and Reuters.
Reuters says a terrorism expert working with the Spanish authorities has told them the warning followed a long-running investigation by the Guardia Civil which was completely separate to the attack in Barcelona.
Rotterdam police have so far not commented on that claim.
On Wednesday night a concert by Californian band Allah-Las in the city’s Maassilo venue was cancelled after a tip-off from the Spanish police.
Rotterdam mayor Ahmed Aboutaleb said he was informed about the terror threat towards the end of the afternoon. The threat said that an attack would take place during the performance and the tip-off was serious enough to merit cancelling the concert, he said.
Band members told the Guardian last year they had chosen the word Allah, Arabic for God, because they were seeking a ‘holy sounding’ name.
‘We get emails from Muslims, here in the US and around the world, saying they’re offended, but that absolutely wasn’t our intention,’ singer Miles Michaud told the paper.