He's an employee of ESPN. He has to be somewhat objective at times.
End of story. Name one other ESPN writer is openly a fan of a team?
He's never rooted against the celtics, or hoped they do poorly. Just because he didnt like Sheed (who does, except for the playoffs) doesnt mean he's not a Celtics fan.
You don't have to drink kool aid to be a celtics fan, especially when your job is to be a sports writer.