Not really sure how else to unconfuse your logic here. If Apple's expectations were low where you say they underestimated, then it is exceeding their expectations. Whatever logic Apple used to decide that number doesn't matter. They expected sales to be X, but the demand is >X. I seriously doubt Apple planned this just get an extra news cycle like this. That's something a start up would do.
It is not Apple planned. But Apple's expectation / estimated are off by a factor of two and it is unusual from a supply chain perspective when they are usually extremely well done if not the best in the industry. Especially for Mac.
They have also not stored enough unit before launch. The wait is nearly 3 weeks. It is a good problem to have but also a problem that if they are targeting education they only have 2 months to ramp up production.
