He's wrong. You can argue that the GOAT is unknowable, but a true GOAT does exist. I mean, hell, the name is "Greatest of ALL TIME"... emphasis on the all time part.

How can have multiple greatest of all time? That makes zero sense.

It is true that the GOAT is probably unknowable due to the difference in eras, different positions etc...

The only way we could factually, indisputably know the GOAT is if time travel were possible and you were able to run through every single scenario of every single player in NBA history on every single possible combination of players with every single coach under every rule set and then see which player provided the most wins... then we would know.

Until then, it's speculation.