Call it a hunch but i believe it's from rolz origin.

Can be rolz, but there is not much interest in rolz then something new as rANS,, Many people find it close to razor but i think razor has upper hand becoz of dedup

I downloaded some figirl games and compressed them and they were smaller with pzlib + srep + razor, but sometimes the ones of fitgirls are much but much smaller that makes me think of some recode