We used to live in Central Asia, and ds kindergarten insisted that all children napped for 2 hours.
ds at the time was 5 and he hadn't had a midday nap since he was 2. All discussion with kindergarten were pointless, the staff worked a 12 hour day and this was their break. I asked if he oculd take a book in to read while the others slept, and that was also refused.
They asked me to try it. We did for a few days, but ds was out of his mind with boredom, and so in the end we collected him before nap time, and the kindergarten persisted in thinking we were mad.
The only time any of my 4 year olds slept that long is if they were ill.
I would have expected them to try and wake him after an hour. Try and wake him at lunch time, and try and assess if he is OK, or just sleeping. (unresponsive, impossible to wake up can be a blue light emergency!)
But this is one incident and you reaction is quite pfb extreme, and to think of moving nursery over this is extreme. Of course if it is the last straw in a string of things, that is more understandable