Because the coach of the all star team is the coach of the team with the best record int he East as of a certain date (Feb. 6 this year).  So, if the C's lost enough games and the Heat or Bulls won enough games, they could still overtake the Celtics for best record as of Feb. 6.  

The Celtics only have a 2.5 game lead on the Heat so if the Heat win three more games than the Celts, they could overtake us.