Is there something ambiguous about, “was exonerated by DNA evidence”?
Not in this case. He really did not commit the crime of which he was committed and sent to prison for. It was a classic small-town railroading and the cops, prosecutor and judge were dirty as hell. They all got away with it too.
DNA can prove someone was present at a location, it cannot prove that he wasn't.
If you can prove someone else was present, it creates reasonable doubt.
It doesn't mean the first person is innocent: it simply means they are unconvictable.
To "exonerate" is to prove someone innocent - which DNA evidence alone rarely does.