I have a 900k+ prestige base on Solum but never did wanted settlement status. Even all the entrance are locked and sealed and base is completely underground. But one day I was out exploring and put down a campfire to temporarily give me some light and then bam! my small base went from ‘outside settlement’ to having a rank on the planet. Turns out the campfire was just a bit too close to a settlement.
The only way I can think of that beacon wouldn’t count towards being a settlement is if it spans two settlements. It’s possible that you had a narrow area in your claimed plots and your new campfire widened it such that the whole thing was now being detected as a single settlement (instead of two settlements with a “road” inbetween).