Big question would be, at any time before this screenshot was taken, invade/conquer a world?
Even a pre-ftl civilizatrion...
Normally you would get 2-3 factions, but if you conquered any other planets and the pops didn't get purged, they would stay in your empire and thus be counted towards when factions sprung up
this would probably explain why the factions are so wide spread with little for pops in them