The Dark Forest is a related idea, in which mature civilizations are not all destroyed by contact with their equals, but lurk about, in ambush. The mutual demolition alternative seems simpler and more reliable, and possibly more consistent with the evidence.
Dropping a black hole, even a smallish one, into a star would seem to eliminate the central pressure needed to sustain fusion, and turn it off pretty suddenly, by astronomical timescales.
Dropping a black hole into a star would actually cause its power output to increase; the radiation from matter accreting onto the black hole provides sufficient power to prevent the star's collapse. See https://en.wikipedia.org/wiki/Quasi-star for more details on the physics.
"Such a star would have to be at least 1,000 solar masses..."
Although, it doesn't really make sense. Like a puncture in the wall of a pressure vessel, the pressure at the event horizon would be zero. It is hard to see how an accretion disc could form in pure plasma at such density. The fluid dynamics of plasma under such conditions is entirely intractable, so it is also hard to believe in any claimed solution.
But temporarily multiplying the output of a star might work just as well to eliminate a pesky alien infestation.
Reading the paper, it appears they treat the plasma as a gas, relying on acoustic pressure interactions that don't happen in a plasma.
If I understood correctly, and that is conventional practice in calculations about black hole accretion discs, there is a great deal of nonsense published on the topic.
[0] https://en.m.wikipedia.org/wiki/The_Dark_Forest
[1] https://bigthink.com/scotty-hendricks/the-dark-forest-theory...