Given the size of the sun and what it does, and not does to us because the size of our solar system also no clue how that thermonuclear probe would work, or how big it needs to be? But curious!
Anyway, if those guys shoot that just around, how likely is it that our stone age AI and other tech would detect them?
How likely is it they'd even consider us worth the effort?
But I also believe that the stance is unlikely and they hopefully had more caring thoughts for us... like we care for all the extinction of our fellow species on this planet.. ehm or maybe should, but they taste too good and I need my house warm :D
Let's say you're a civilization advanced enough to direct world-destroying missiles at everything 100 LY around you... that means you can reasonably get some intelligence on what you're destroying, and it's probably valuable enough territory to make it worth checking out before you incinerate it. A 100-year mission to go there and, oh, alter the atmosphere just enough to eradicate the dominant species, would be a much better strategy than just annihilating a productive ecosystem...