Why didn’t he move the bees into the green house? He could have thrown a heater in the green house and kept the temperature at 25 degrees. I think he only has himself to blame.
On even a cold day where it is zero or below outside, the sun will warm the inside of my greenhouse up to the mid 50s. If the weather changes to the mid 20s, the inside of my greenhouse on a sunny day is in the high-60s or more. That's enough to move the bees from their winter mode (in which the bees live for months huddled in a ball in the middle of the hive expending minimum energy) to normal mode (in which the bees live for only about 50 days, flying around, looking for food, and expending lots of energy). It seems like a good idea, and I considered it in February for my surviving bees, but it would almost certainly kill the bees.
I could open my greenhouse to the weather, thus regulating the temperature better for my bees, but then I'd kill my greenhouse winter crops.