People use the word 'bomb' in conversations on the phone all the time. Nobody is getting their calls disconnected for saying that, I assure you. It was a strange coincidence - a fault on the line or similar phenomenon.
Agreed, it's an incredibly popular word, and even if calls were just being dropped in train stations, it would still be widely known. Plus, what would be the advantage of dropping the call, and allowing the person to redial? If the call is being monitored, wouldn't it make more sense to send the audio to security for review? If they're calling from a public phone, you could activate a silent alarm so they're randomly selected by security, or simply redirect security cameras to their location.
