There are so many potential explanations for that phenomenon:
- hot tap water has more mineral contents than cold water which helps form the initial ice crystals
- hot water in a container creates a convection effect on the air surrounding it, thus creating an influx of cold air around the container, helping cool more quickly
- hot water in a container melts the ice/snow under it (if the experiment is conducted outside), reducing the insulation with potential colder ground
- thermal motion of hotter H2O molecules may help create accidental collisions that trigger the formation of ice crystals
- hot tap water has more mineral contents than cold water which helps form the initial ice crystals
- hot water in a container creates a convection effect on the air surrounding it, thus creating an influx of cold air around the container, helping cool more quickly
- hot water in a container melts the ice/snow under it (if the experiment is conducted outside), reducing the insulation with potential colder ground
- thermal motion of hotter H2O molecules may help create accidental collisions that trigger the formation of ice crystals