Do you have inside knowledge we're unaware of? Otherwise it's hard to say "in reality...." $1B is plausible, but much more questionable given this article.
The key part:
because GM GM is being very narrow in how it describes the deal value. The $581 million (or $600 million, whichever you prefer) is the cash and stock that actually went out the Detroit doors during GM’s second fiscal quarter. Not included were a variety of other things, including cash still being held in escrow, expected earn-out payments, employee retention packages and other expected employee compensation (particularly for those with unvested shares at the time of acquisition).
What Primack describes would be like buying a house and claiming its price is what you paid as the down payment.
I consider this article to be pretty poor, if they wanted to actually find the real price, they could've investigated some more instead of trying to infer from the earnings' reports.
[x] I believe he was also an investor in Cruise