That one wasn't an actual unification as the belt wasn't on the line due to a dispute, and Tyson was stripped of his WBC belt shortly after. This content is protected
The WBC champion beat the WBA champion to unify the WBC & WBA titles. Tyson became unified champion. Yes, Seldon wouldn't have become unified champion had he won, but he lost, so the fight resulted in unified titles.
Rummy's videos are some of the best work on YouTube...although I disagreed with him putting Holmes ahead of Lennox as the best since Ali. It's not a wide margin, but Lennox's resume is better overall.