The data being referenced the past couple days was released by the market research firm
1010data. They clearly stated the source for their October figures as:
"The data comes from millions of U.S. consumers who voluntarily share their shopping histories. The report did not take in account customers who purchased their tablets in brick-and-mortar stores, such as Apple’s retail stores or Best Buy.
The survey lumped together both tablets and variants of the devices known as laplets, 2-in-1 PCs, and detachables."
That would be online sales only, and not Surface specific and would include models like Lenovo's Yoga along with Dell... Asus... or anyone else who makes an applicable device, regardless of WinBeta choosing not to provide those details.