YES.........mfgs like to 'include water heater tank' in Fresh Water Capacity (Totals)
We have 70 gallon tank.......Sticking hose down fill tube and hose on full (50#) it takes roughly 10 mins to fill tank until water is running out overflow tube behind rear tire.
But that is AFTER I shortened fill tube....it was too long and had a big 'U' in it and would sag then blow water back out fill opening.
Fortunately fill tube, vent line are accessible thru removable panel in kitchen....water heater/water pump also.
Hope you can access it...check out how fill tube is run and vent line..if either kinked/sagging can casue issues filling tank