[flybouy]

The HWH - either the valve was not in position correctly or the check valve in the line is stuck open. Leaving the antifreeze in the hot water tank can create an issue as it's corrosive to the metal in the tank.
The issue you have with winterizing the way you did (via the freshwater tank) is:
That method requires a LOT more antifreeze
Now you have a fresh water tank with antifreeze in it that will require repeated flushing in the spring to remove the taste and the chemicals.
Most people will use the pump to directly pump the antifreeze thru a "winterizing pick up tube". That's a plastic line typically found close to the pump connected by a "T" fitting and a valve (like the winterizing valve on the HWH.