Well, this is all positioned as "possible technosignature," there's not some black hole orbiting around a planet that we've seen that has us going "that's weird

Well, this is all positioned as "possible technosignature," there's not some black hole orbiting around a planet that we've seen that has us going "that's weird must be aliens." Though, a black hole of the size we're talking about is in and of itself potentially evidence of aliens - as noted in the article, they would evaporate within a year and a half without a constant influx of mass. Most places where you would find a black hole that is accreting matter is going to be a place where there is enough matter for it to become significantly larger, and once it's away from places rich with matter, space is emptying enough there's basically no chance it's having that much fall in.