Perhaps it has to do with the increased turbulence in the hotter fluid? This would be a result of the higher saturated vapor pressure of the liquid leading to g

Perhaps it has to do with the increased turbulence in the hotter fluid? This would be a result of the higher saturated vapor pressure of the liquid leading to greater evaporation/boiling. Even as it cools down the higher temperature difference between the hot fluid and room temperature should produce a more turbulent boundary layer along the surface of the water. The turbulence will reduce the thermal resistance associated with laminar surface air films on colder surfaces, which would normally be insulating surface, so you'd get a faster heat loss then with a more stagnant layer of cold water.