Let's assume that the events in the story are true. Even if true, it does not mean these guys were doing a dry-run or were affiliated with Al Quada, etc. It does not mean they were planning anything other than what they did. But they can still be considered terrorists, IMO. If this unfolded as described, it could well be that their goal was to instill fear and terror into the people on the flight, or the people reading about it here.
In their ignorant jihadist mentality, anything they can do to inconvenience the great Satan is a victory for them. If the only thing they accomplished was to cause a flight to be canceled, and to cause people to fear flying, then they have struck a blow for their death cult. The musicians on Annie Jacobson's flight and the Flying Imams were doing the same thing. Plus they get to play the "aggrieved minority" card and clean up in court when our gutless/traitorous judges and the ACLU bend over backward to accommodate them.
If this really happened, it was a terrorist attack and it succeeded.
I agree, if it was their intention to instill fear, they were committing an act of terror. If that is the case, the TSA REALLY messed up by letting them back on the plane without interviewing other passengers/crew.
I don't think that was the plot - they could have created similar fear without exposing themselves by a simple bomb threat or such.