This sounds like nonsense to me, and a lot of people grossly exaggerating their self-reporting.
27 hours is very very difficult to find in a week. It equates to more than 5 hours per working day, or 3 hours per working day plus 6 hours per day on weekends. That is absolutely not happening, and definitely not with 4/10 teachers. I used to live with teachers and if I saw them do an hour a day that would be a lot.
The whole trope of marking work at home might be a thing - but generally that isn't 100% concentration. They're usually watching a film or TV. Is that really a fair way to gauge working time? You also sometimes get highly highly motivated people in all professions who decide to do additional work at home because they're dedicated or perfectionists or whatever - that can't be realistically counted.