O'Sensei never "dodged bullets." When the guns were fired, he wasn't there.
If that is true then there are only two possibilities.
1) He started running before they took the shot.
2) He started running after they took the shot.
If nr.2 is true, then he's twice as fast as a Neo in Matrix. If nr.1 is true, the shooters were not doing thier best.
Is there a nr.3?