A lot of people think he took the shot and just said "The heck with this." Truth is Jersey Joe blacked out in the middle of the count (Somewhere between 4-8/9). He later admitted to this.
Marciano came out much differently than in their first fight, and Walcott had no answers to it. He caught him with a beautiful sneak right uppercut that he never saw coming, and after that it's possible a discouraged Walcott decided to pack it (though only he would know). Very impressive and underrated win by Marciano, which is too often dismissed simply because it happened to be Walcott's last career fight.