I don't think he's a pastel pied. He's not really any lighter than my pied, what tricks you is the lack of black in his pattern. He's got lots and lots of brown and a minimal amount of black, that's what makes him seem lighter.
Let me see if I can show you what I mean. This is a body shot of my pied boy. Right off the bat he seems a lot darker because he has so much black in his pattern:
But now watch what happens when I crop the picture to eliminate the black:
Can you see how minimizing his black makes him suddenly appear lighter? I think that is what is up with your boy. His crazy pattern doesn't have as much black as most, and it fools you into thinking he is lighter because there isn't as much black to draw your eye.
Now it is possible he's a pastel pied. If his mom was a super browned out pastel, it just might be. But I tend to think he's just a normal with a killer pattern.
Gale