Are items being listed in stock so that people place their orders while the store/company knows they are out of stock? How long does it take to update availability?

What if a store purposely kept items listed as “in stock” on their website for delivery, so that you placed your order only so they could substitute those out of stock items with whatever they had on hand? I ordered this morning and one item was listed “in stock” and ready for delivery only to be told it’s actually out of stock. But when I check back at 5:30pm it is still listed as “in stock” and eligible for delivery in as few as 28 min. Really Walmart? They knew this am and probably before that, this item is not available…but they have not updated it in their system. I also had several other items that I ordered today that were “in stock” that they did not have. And every order I place seems the same thing is happening. I am starting to suspect that it is not by accident.