https://www.euronews.com/my-europe/2026/05/24/flotilla-activists-return-to-spain-sparks-clashes-and-arrests-as-israel-slams-hypocrisy

According to police sources, the incidents occurred as six members of the flotilla, who had just landed, were posing for the media and blocked one of the arrivals’ exits at the airport.

So the reasoning is that the group picture “blocked the exit”.