So why were the guys not arrested and interrogated on arrival?
From the article none of three broke any laws or regulations. I didn't see anything about them refusing the orders of a flight crew member.
But, at the least they should have been detained and questioned, under the threat of being placed on the 'no flight' list.
"Tell us what you were up to or why you did what you did or this is the last airline flight you will ever have in the US?" That sort of thing. There very well could have been a completely innocent explanation for their actions.