Even if you discount the possibility of an intentional threat as silly, this could have been a warning from someone under duress. Turning around was the right move.
How does that scenario work? Someone's under duress because presumably there's a terrorist on board. He lets the crew know there's a bomb onboard. The plane turns around, and the terrorist... lets the plane land safely?
OK maybe the bomb blows up when it crosses some longitude, because this is like the movie Speed, and turning around means the plane never cross that longitude..
If you mean another type of duress, naming your device "plshelp-[seat number]" would be a hell lot more effective..
How does your scenario work? Someone anonymously shouts BOMB ONBOARD and the plane just continues to its destination? "I guess they can blow us up whenever, so might as well keep going..."
Wow, ok, because someone anonymously shouting (how the hell does that work?) is the same as a Bluetooth device broadcasting its name, which happens to be "Bomb"...
Honestly I didn't think about that. Maybe they didn't either. Good example of why seeing something vaguely threatening and out of the ordinary is a reason to turn around, even if you don't know why exactly they'd do it.