Mizuno and friend repeatedly stuck their hands in a bucket of boiling water to prove the 'heater' was still working. Is that really what you're saying?
The power was turned off on April 22. The thermocouple pen recorder trace (which is in the book) showed that the temperature began to fall.
On April 25, Mizuno and Akimoto saw the pen recorder trace was back up to the high temperature, above 100 deg C. They held their hands near the cell and confirmed that it was very hot. They decided to move the cell from Akimoto's lab to Mizuno's lab. They could not touch it, because it was too hot. They wrapped it in towels, moved it to the other lab, and put it in a bucket of water.
So, yes, I am saying they held their hands near the cell to confirm it was hot, and to confirm the thermocouple was working correctly. Why does that surprise you? Why do you say "is that really what you are saying?" How would you confirm that a 10 kg steel object is hot? Is there anything wrong, unusual, or unscientific with using your sense of touch to confirm that an object is hot and the instruments are working correctly? It is common sense to do that.
The next morning the water in the bucket was gone. The cell was still radiating heat, and still too hot to touch. The thermocouple was not connected to a pen recorder, but the voltage indicated 100 deg C.
The next morning it was the same way. This went on for several days, until the cell finally cooled. When it cooled, both sense of touch and the thermocouple indicated it was at room temperature, so there was nothing wrong with Mizuno's sense of touch or with the thermocouple. The water no longer evaporated overnight. For details see the book, or at least see the introduction:
(It was not a "friend," it was Prof. Akimoto, an expert in particle detection.)
Not an error, a high airflow rate over the water.
There was no airflow over the water. The bucket was sitting in the lab, on the floor. I have been in that lab and seen the location. There are no fans there, and no rats either. Also, the building was not "abandoned." I don't know where you picked up that bit of nonsense, but it was not. Neither was the first lab, where the cell remained hot for 3 days after the power was turned off. That was in Akimoto's lab, in the linear accelerator building. It is deep underground, with a very stable temperature and quiet conditions. There are no fans there.
Also, you have to explain why the water stopped evaporating after the cell finally cooled down. That is, after the thermocouple and sense of touch showed that it was at room temperature. Was that a coincidence? Do you think the cell temperature had no connection to the evaporation? Why did your imaginary, non-existant fan stop working after the cell cooled down?