out of bounds because of your hair ?

Yes he was, it was pretty obvious. Had he not been touched, he would've stayed on his feet.

Check out the video at:

http://www.nfl.com/gamecenter?game_id=29517&displayPage=tab_gamecenter&season=2007&week=POST18

Pause it at 2:49 / 2.50, it's clear that Mathis and Davenport stumble on each others legs even after Mathis has possession.

 

You are considered down if any part of your body touches the ground other than your hands or your feet. You'll hear Madden say quite frequently,"One knee equals two feet" when a player lands inbounds on one knee then slides out of bounds. Same principle.