The two standard product classifications is "7 inch tablet" and "10 inch tablet". Those are standardized names, even though there is really no 10" tablet and really no 7" tablet. The iPad is grouped in with 10" tablet even though the screen size is slightly less than 10".
Similar to how the iPhone 5 has a 4" screen, but it's much smaller than a normal 4" screen in width. That's the product category. "7 inch tablet" as a market segment doesn't mean exactly 7 inches. Just because Apple said they'd never make a 7" tablet doesn't mean their product doesn't compete in the 7 inch tablet market.
I would say that the iPad is not a tablet because it doesn't have a x86 processor nor does it run Windows Tablet Edition. The iPad is a larger smartphone, and the iPad Mini is a smaller larger cell phone.
I hope I don't sound ridiculous because someone miscategorized the iPad in the same category as Windows XP Tablet Edition.