25,000 feet is very high for a mooney. Sounds like he was trying to fly as high as possible, then passed out, the plane kept climing then entered a spiral dive.
I'm sure a lot of pilots go above 10,000 feet, or even 14,000 without oxygen. It's a tricky subject. It's not like as soon as you go about 14,000 you will pass out, but you do need to keep track of how long you've been at such a high altitude.
I may think twice the next time i'm tempted to try and find the absolute ceiling for an aircraft.