Selfin, they have a man in custody. Whether he was genuine or not, there is tangible evidence that he threathened to blow up the airport.
What next? Do you suggest that Fire Brigades don't attend 999 calls because they think its a hoax? No matter how serious or not a nutjob like this is, he must be taken seriously until the threat is neutralised. Shame, in a civilised society, but it's fact.