IF water pump internal check valve leaked (allowed backflow thru pump) water could flow into fresh water tank when connected to city water. Also IF 'fill' valve leaked thru/wasn't fully closed water would also go to fresh water tank.
Tank gauges........hehehehe
Notoriously inaccurate. Plus until level actual gets up to FULL sensor (if sensor is in correct place) 2/3 will be lit.......so with 60 gallon tank that could be as much as 20 gallons between them.
This "small hole just over the passenger side rear stabilizer jack". Is that the overflow tube OR just a hole in underbelly cover?
Overflow should be a tube sticking thru underbelly cover.
If just a hole....should open up underbelly cover and inspect. Least its clean water but still water causes damage and mold/mildew issues