I think the level of suspicion is simply about how many boxes get ticked.
- changing seats, tick
- sitting up front near to the cockpit, tick
- in a group, tick
- religious/ethnic group, tick
- false passport (in reference to the parallel discussion), tick
Remove 1 or 2 of those ticks and there would normally be no problem. In this case a lot of boxes were ticked and someone rather than quietly informing TSA for a recheck, overreacted.