In the second scenario the Russell's teapot satellite the Soviets put into space would have picked up the uptick in US military Comms.
Maybe they kept it quiet to not reveal the satellite was still operational? I doubt it given the current situation, mostly likely it'd be all over telegram and we'd have known about it.
> The Navy began listening for the Titan almost as soon as the sub lost communications, according to a U.S. defense official. Shortly after its disappearance, the U.S. system detected what it suspected was the sound of an implosion near the debris site discovered Thursday and reported its findings to the commander on site, U.S. defense officials said.
LOL. C'mon man, you're the only one here who thought this was some kind of super secret capability. My entire premise is that this was a logically foregone conclusion based on what we know of their decades-old systems and the laws of physics with respect to how sound travels in water.
As for why they revealed their foreknowledge now? I don't speak for the military, but admitting to it vaguely, well after the fact is a significantly different situation than talking about it at the time and making it actionable intelligence. Furthermore, something may have leaked to a journalist, who then pressed them to make some kind of answer.
Maybe they kept it quiet to not reveal the satellite was still operational? I doubt it given the current situation, mostly likely it'd be all over telegram and we'd have known about it.