The habitable zone doesn't mean "anything inside supports life, everything outside doesn't". It specifically means "the light from the planets sun is in the ra

The habitable zone doesn't mean "anything inside supports life, everything outside doesn't". It specifically means "the light from the planets sun is in the range to support surface-level life". If a distant moon in our solar system has a liquid ocean that A) doesn't mean it's water or anything else sane and B) that habitable zones are poorly defined. Liquid oceans generated by orbital- or geothermal activity aren't covered in the habitable zone definition and aren't very useful as they usually require a parent body to provide energy to heat the ocean (jupiter for example) but just not enough to boil it off the moon.