He won the New York State Championship from Mathis, but that title was only recognized in New York and a few other states. So, I wouldn't say he was officially the champ until he knocked out Jimmy Ellis.
After Joe beat Mathis,I consider him to have been the number one ACTIVE heavyweight at the time. Most could see that he was already better than Jimmy Ellis.
I can't remember the odds for the fight, but Ellis was given a good chance ,if I recall correctly. Mathis was not even ranked he had a string of wins over pushovers. The NY State Commission got it wrong that time . I think it was a double header with Benvenuti and Griffith, in MSG ?
He won a version of the HW title that was recognised in NY...Mass....Maine...and a few other states when he KO'd Mathis in 1968...