I have no idea, but it honestly is a great question. Tell ya what, instead of posing it here why don't you reach out to NASA and find someone to ask. While you're at it ask them how they know the light from some distant star, galaxy or whatever really took X number of light years to get here and for that matter how they know it's the same light and not light from some other source.I didn't read all that, but if the black hole is 250 million light years away, how can they be certain that what they are listening to is actually coming from that black hole?
What have they got that is so precise in its "direction" to hit any object for listening at that distance?