"Probably" is an overstatement. There are many possibilities, and there's no way to assess the likelihood of that one relative to all the others. As I said, it could just as easily have arrived after they already abandoned the planet for other reasons.
Or maybe the Hirogen weren't even native to this system, but took its name or became associated with it for some reason. Maybe it's like the historical use of "Gypsy" as a slur for the Roma people, based on the mistaken belief that they originated in Egypt. Maybe some other species called them Hirogen because they erroneously thought they were from this star system, and the name just stuck. Or maybe it's like how, in my novel Ex Machina, I explained that the Betelgeusians weren't actually from Betelgeuse (a supergiant star way too young to have inhabited planets), but, like Ford Prefect, came from a small planet somewhere in the vicinity of Betelgeuse. In my conception, they'd long since abandoned their homeworld and become nomadic spacefarers because they knew their home would be destroyed when Betelgeuse inevitably goes supernova. So they were named that because their "home" was the sector of space around Betelgeuse. Maybe the area around the Hirogen system is called the Hirogen sector, and the species we call the Hirogen were from some other, less notable star system in that sector.
Or maybe... use your imagination. The first idea you get should be the starting point, not the stopping point.
