I've looked up the definition of "bully" - and I have to admit, they all define the word in pretty much the same way you just have, which surprised me, as it wasn't my sense of the word "bully." It seems to me, though, that by that definition, any police action in which the suspect doesn't just acquiesce and come meekly along, is an example of Bullying - which really stretches my sense of the word.
It should be noted though, that in the case of the FBI seizing the equipment, it turns out to be the case that Roberts actually was guilting of making the threat/joke about messing with the airplane's EICAS system, so it's not clear to me that we can claim it was an "unproven alert."
You can always seize the equipment, perform an investigation, and then return it. But if you fail to seize the equipment, then the suspect can wipe it/destroy it if you later determine you do need to review it.
I'm guessing the FBI (any police agency), in this situation will follow the "Better safe than sorry" approach.
And, as to how you can avoid having your shit seized by the cops - most of us were taught at the age of 5 not to use the B word in an airport - just extend that logic to not making jokes about messing with the aircraft safety and you should be fine.