Established a colony in a high warning beacon remnant system, destroyed the nexus, and something weird happened.

I established a colony inside a remnant system for the purpose of establishing a colony in between my first colonized system and a hypershunt system. Now once once the colony has been established, I snuck through ordos and destroyed the remnant nexus to prevent anymore remnants spawning. Now I left the system for a bit, then returned only to find there aren't any remnant fleets left. There are still a good amount of them before I left the system, and now they're all gone. I haven't even build a military base in the colony or a station. Is this normal? Is there some update I missed? I only got back to this game a few months ago so a lot of things are new to me.