It's not Frontier. You'd know if it was because they wouldn't be subtle about it with a couple of settlements. Generally speaking, who would notice or care (obviously you do, but I'm thinking in regards to the entire playerbase) What they'd do is flip the whole system if it was to suit the narrative. If it was Frontier staff doing it in their spare time (bit weird having your job as your hobby, but it takes all sorts) that's up to them. On the grand scale of things what faction controls what means very little so I don't see why they should be stopped if they're basically doing what we could do.
More likely though is what you have is a popular area for players to be in because of history and you've been hit by random traffic. With they way settlements work, you can't defend everything.