I was not able to finish Blindsight. It is too pretentious for me, it ignores what state of art was at the time. Let me quote an old comment [1] of mine:
Do you know that current 1sqkm radio telescopes produce data that can't be processed at real time in any cluster environment in use at 2015-2016? They scan skies at precision I just cannot express in words, let's try math.
https://www.skatelescope.org/uploaded/2950_31734_2007_IAU_Ta...
"...with a resolution of few micro-angular-seconds..."
sin(5/57/60/60/1000000) equals to 2.4366472e-11. It is sine of roughly 5 micro angular seconds (1 radian is about 57 degrees). 1/sin(5/57/60/60/1000000) is roughly equal to distance where current SKA can distinguish 1 meter radio-emitting object and it equals to about 41 million kilometers - a fourth of the distance between Sun and Earth.
These Firefall objects just won't be "unnoticeable until their entry to the atmosphere" in the state of the art sky scaling systems of Blindsight's time.
[1] https://news.ycombinator.com/item?id=18381870
Despite me being very unrespectful to Watts works, I recognize his influence. So, what is this Blindsight-related-story you are talking about? I read many of them and I cannot remember any that resembles your description.