No. That is just an inclusion.Re-read it. He says that in his 5 years, wizards and specifically bladesingers are the only class that he has played past level 4 without multiclassing. He is talking about the entire class there, not specific characters. Then he mentioned a specific bladesinger he has multiclassed with that is past level 4. That's contradictory.
He has played many classes. He always multiclassed them if he played them beyond 4th level. The only class where he did not necessarily do so was the wizard.
That does not mean he didn't have a wizard that also multiclassed.
But you can also read it your way.
But even if you read it your way, it is possible that he played the wizard up to 6th level without multiclassing and then multiclassed...