I read a few articles about this one. One of the key moments came when a doctor had a potassium test performed, and saw that they were normal, indicating that heart function might be able to resume. What I read was that his body was frozen at just the "right" rate for it to survive, but it isn't clear why his brain wasn't severely damaged.
The standard of care for hypothermia has come a long way for first responders but is still uneven in the hospital setting. Hopefully this continues to improve.