Being put in handcuffs and kept in a cell for several hours is not the same as being detained at a traffic stop to answer a few questions. And no, I don't think most objective human beings want to live in a police state where carrying arabic flash cards and a perfectly legal book is sufficient cause to be inconvenienced by the state in such a manner.
No, legally, they are not. Any time you are in the presence of a law enforcement official and you are not free to leave, your person has been seized for purposes of the Fourth Amendment. From a Constitutional viewpoint, both arrest and "detainment" are a seizure of the person, and legally indistinguishable from an individual rights standpoint.
Second, how are the TSA agents stopping people from leaving until local PD arrives, if not by making arrests? The moment of arrest is "determined by whether a reasonable person under the circumstances would believe he was not free to leave. United States v. Mendenhall, 446 U.S. 544 (1980)
There are stark legal differences between arrest and detention. TSA agents are authorized to detain, but not arrest, suspects. The bar for detention is lower, and detention may be performed by people other than sworn peace officers. Even private security officers - such as those at casinos in Nevada - are legally permitted to detain people for the purpose of notifying the police if they believe a felony has occurred on the property. NRS 171.1235
By contrast, an arrest may only be performed by a peace officer with probable cause to believe a crime has occurred. Detained suspects do not have to have their rights read to them, whereas they must be read to arrested individuals. Detained suspects are either arrested or released usually within hours, as was the case here.
Detention and arrest are vastly different things, both legally and practically, that are used for different purposes. The system worked here: he walked into an airport displaying many red flags. He was detained for a few hours, determined not to be a threat, and was released.
What were the many red flags? It looks to me like there was at most one: the flash cards. (And IMO zero, because the idea that having "bomb" written on a piece of paper makes someone suspicious is ludicrous.)
