But it's the exact kind of tool with which one would carry out the threat he made. And TFS said they seized his "storage devices" also. I would not be shocked if they took his phone, and for the same reasons. Actually I'd be shocked if they didn't.
Your analogy is even more torturous. You said "acquaintance." But he didn't say this quietly to someone who knows him. He broadcast it on twitter. To anyone who happened to be reading.
And if someone on my plane did start talking about making weapons and stabbing people, I would absolutely report that person to the flight crew. That is weird. That is weird, suspicious, dangerous behavior.
This was the guy's tweet:
“Find myself on a 737/800, lets see Box-IFE-ICE-SATCOM, ? Shall we start playing with EICAS messages? “PASS OXYGEN ON” Anyone ? :)”
Your sample dialog about the tray makes it sounds like a concern that someone else might do something bad. But this guy was using first person pronouns. Not that "someone else could do something bad" but "shall I do something bad?"
So let's rephrase that for your tray analogy, where your seat mate (that you don't know) leans over and says to you (or even to a friend, but you clearly overhear), "Find myself on this plane...let's see, a tray I can craft into a knife? Shall we start stabbing people? "Bleeding out" anyone?"
Yes, I'd report that. Weird as shit.