You should just read the release from Apple, it explains it.
It is the number of iPads that went into the hands of customers in the first day. So it includes units sold in stores as well as preorders that were received by customers on Saturday. Considering that 3G units don't ship for a few more weeks meaning it's only some of the preorders, whether you call it "spin" or not, getting 300k units into the hands of customers in one day is pretty damn impressive.
Actually it says that 300k includes units delivered to stores. Meaning whatever stock is left in Best Buys and Apple stores unclaimed and unsold IS included in this number.