I wouldn't say premature, he was 40 years old for gods sake. He just wanted to get out of the business before before he got too old I guess.
Just maybe Lewis feels that he beat Vitali so there is nothing else to prove. He was the one that caused those cuts.
Being scared has nothing to do with it, I mean come on! He's a professional Boxer and one of the best ever. Even Ali has never fought anybody with skill, that had that type of size and strength advantage.