Earlier quoted context omitted.
Indeed he may be, but the case of Herrera v. Collins is pretty clear - laws are about procedures, not facts. If someone has been found guilty in a trial, and there were no flaws in the prodecures followed, then it is not unconstitutional to follow through with the punishment, even if later evidence shows the person is innocent. More importantly, it would be procedurally problematic if convicted criminals could appeal…
Convictions get vacated when an alternate perpetrator is identified or confesses.
The hard part is how to establish that alternate confessions or new evidence are really significant (as they indeed sometimes are).