You should get super angry about a mistake done by (like a poster said) a "low-paid retail employee" I used to work at Best Buy and you know why we made mistakes (not too often, but it happened)
1.) We ARE human.
2.) Besides Apple we were the biggest reseller of Apple Products but Apple rarely ever let us know when we were to get a shipment of theirs so we had to guestimate as best we could when people order an item. Add the fact that we had thousands of orders to create and ship everyday and even when we got that person what they wanted, we often got slammed and yelled at for it taking too long, being too expensive, or they just were "God's perfect little *entitled snickerdoodles" and we failed at being perfect.
Your situation is easy to solve, make sure your order is cancelled and your money returned to you, then go to Apple or Best Buy in store and buy your iPad then. Or be one of those people that made BBY employees ecstatic by being one of those: "I'm never shopping here again" customers. lol
I've worked in retail for about 10 years... I'm happy I'm out now, as I don't miss being verbally destroyed.
Also guess what, Best Buy have messed up my orders dozens of times (last iPad order was messed up 5 times, and while I was not happy... I didn't freak out cause it wasn't the end of the world.)