Your theory has a hole. Customers didn't know the supply ahead of time. People would have lined up whether apple had 10MM phones or 2MM phones.
Yes customers didn't know the initial supply number, but scarcity is something you cannot lie about.
It's sold out everywhere, every customers are limited to purchase up to 2 iPhones. People need to book their purchase earlier or they run out of stocks.
Whether artificial or not, that's scarcity for you .. And it looks good on headlines "Sold out anywhere on Planet Earth" and for the coming years it will always be.
Do you go hunt and lining up for a new product of Pepsi? You sure don't, you can get one EASILY on your local retailer, or even mom and pop store.