This characterization isn't entirely unreasonable. Isn't Musk objectively the richest businessperson ever in nominal dollars? Inflation-adjusted, I think only Rockefeller or Carnegie may come close, but the variety of businesses Musk has is impressive, and it appears he is just getting started with a long way to go.

Inflation-adjusted I believe Rockefeller was worth more than $400b at the peak of his wealth.

The Walton estate now is worth over $350b, but it’s not a fair comparison as it’s had much longer to compound.

The other thing is that while SpaceX is incredibly successful, the other companies he’s started aren’t. Tesla (despite its massive growth) is in a market of rapidly growing competitors, and he’s on record saying the company lives or dies on tech his own engineers have suggested in court isn’t coming (FSD).