The point presumably is that the valuation in a round is paper money. Whereas Elon's group have just offered cash, so they've set the actual value. The law might only care that the non-profit gets a market cash value actually bid, not the speculative value that it could have based on multipling how much some shares were sold by the number of shares.

Actually, OpenAI's for profit was going to buy itself from the non-profit at $40 billion. So this at over twice that is a much more attractive offer.

And a valuation in a funding round is not the same as a cash offer for the full amount. Otherwise every startup would be liquid.