That is, the coded message serves no intelligence or military objective. It sounds to me like the government concocted this idea because they felt they should be doing something, anything, no matter how useless( * ).
What's a hostage supposed to conclude from hearing, "19 people rescued. You’re next. Don’t lose hope". Should I run? Run now? Hide in the jungle? Run when the rescue starts? Stay put? Fight during the rescue? Don't fight? If you asked 10 different people what specific action you're supposed to take based on this message, you'd get 10 different answers.
If this message had any tangible effect, why aren't there any first hand accounts from the hostages explaining what they did differently as a result of hearing the message?
So 3 million people heard this song, yet the only ones who understood it were some of the hostages? Not one of the several thousand militants and no one in the public decoded it? This just proves the point that it's un-actionable. Case (1): Lots of people got it besides the hostages, but there's nothing to blow the whistle on. It's not as if the message says, "Raid at dawn". Case (2): Nobody got it, which also implies that the message had no effect.
( * )If the government claimed that the message was simply a way to make the hostages keep up hope, then OK (though it still seems like a lot of expense for little gain). But they're trying to make it sound like a big intelligence or military coup, which it is not.