How do random custom xenotypes work?

How do random custom xenotypes work?

I have a handful of mods, one adds a faction that has pawns that spawn as a "random custom" xenotype. What does that actually mean?

Also I have this mod (https://steamcommunity.com/sharedfiles/filedetails/?id=3219379049) that adds fantasy races/factions to the game, would they be counted as "random custom" xenotypes and spawn with this faction?