The pizza Bitcoin story is not about a mere $1 billion.
The guy that sold his Bitcoin for pizza, did multiple transactions (detailed in that forum thread), not one. Somehow this part is lost to history when the story gets told.
He liquidated tens of thousands of Bitcoins.
The tally is a lot closer to ~$4 billion at $82k per coin.
Then there's the question if it would have gotten to 4 billion today if he hadn't used it back then...