It's because I have a big, huge, natural reflector right behind me that is lighting his face (ignore my goofy, squinting face --I'm facing straight into the sun --, I just want to show you where I was and what was directly behind me):
The bright rock acts as a reflector. Look for such reflectors when you're out and about. It can be a large wall, sand, snow, mirrors, slides at parks, etc.
Here's another example of my youngest son climbing on a bright rock. It's reflecting light right back onto him. Natural lighting at its best. :-)