I don't see your point. How does horizontal only scrolling make it clear that only a touch screen was taken into consideration? I seem to be able to scroll left-right just fine with my mouse. I agree that scrolling in Windows has typically been vertical in the past but disagree that the departure from that means only a touch interface was considered.... Clearly the designers had touch screen (only) in mind. ...
Are there functions that can only be done using touch, that can't be duplicated using a mouse?