Maybe each powerful galactic civilisation has been driven to the same point as Petey and needed to create safe, tame, Pa'anuri; and that is where the entire population has come from. One or more for each failed attempt.

Things that fit with the Pa'anuri maybe not being the masterminds behind all this are that they somehow have an Andromeda core device and long guns despite that being 'impossible' for non-baryonic life without baryonic allies.

Also, wasn't the "50,000 years working with the F'Sherl-Ganni" a trick to get them to destroy themselves without initiating an extra galactic effort?