I inherited these planets. I think the colonizer ship's AI was at war with the owner of the planet. Anyway.
I just find it weird and wonder if it's an AI issue or some mechanic I was unaware of. The planets seemed developed well enough that they weren't "just" colonized, i.e. they've been there long enough for that other AI to realize there was already someone there. If anything, it should have been transport ships. Hard to tell, but I'm reporting it here anyway.
Save game is here