Link to auction
Gorgeous photo, and although I'm not even a newbie in the field, I think the high price was due to a confluence of a few factors...
1. early, recognizable, type I Mickey Mantle photo
2. connection to the regional cards and yearbooks, as mentioned
3. Henry Yee auction
4. described as being a "one-of-a-kind" exemplar
5. originated from the Stevens collection