As usual there are insufficient details to come to any conclusion.

Scenario 1: the students were sitting quietly in their seats and the crew decided to arbitrarily play the FWB card.

Scenario 2: the students were engaged in unusual and/or non-compliant activities on the plane.

Or somewhere in between. Although it is possible they were completely innocent and innocuous (scenario 1), my feeling is there was more to it to require a 4-hour investigation. This was a lot more than re-screening.