The story doesn’t make sense to me. I’ve showered almost everyday for the past70 years in water from a water heater that never reached 60 degrees C (140 F). Most people in the US could also say the same.
Similarly, the water in a heat pump, even the heat pumps that generate domestic hot water, never have the heat pump water mix with the water in the hot water heater. This makes the temperature of the primary heat pump irrelevant.
I have installed and used heat pumps since 1988, that first one being a ground water heat pump that also provided domestic hot water. It pulled 52 degree water from our well, and dumped the colder water to a lake. My present heat pumps are air to air.
I'd probably have gas heat to supplement the heat pump if I didn't have solar and battery to power the home through most nights. And the heat pump water heater giving me free cold air (see post 11) that I put into an air receiver for my home during the warm half of the year, is efficient in part because my HVAC is a variable speed heat pump with var speed air handler. In other words, my HVAC is almost always running, even if at low speed. So just about any time of day that my water heater gives me free cold air, my HVAC is running to draw in the free cold air to spread through the house (so that my home heat pump can be in low speed a few more hours of the day and not have to work as hard making cold air for the home).
Where do you draw air from for your heat pump water heater? Mine has a duct to draw air from the attic (usually warm air, or even really hot air in my Alabama attic). Thus, my water heater heat pump doesn't have to run as long to find enough heat energy to heat the tank. So the attic often has free heat energy that's used to help heat the water tank, and the water heater give me free cold air that I use to help cool the house. The water heater is efficient, and the HVAC is efficient, but the two work together better than the sum of their parts.