Depends if you think you're moving the document, or moving the viewport. Touchscreen behaviour is touching the document and moving it up, while your view remains the same. Traditional scroll behavior is that you're moving the view of your document down while the document itself doesn't move.
Either way, one method is "the original one", the other method is the opposite, or reversed, from the original method.
I don't really care either way - it's a setting so you can use what you prefer.
But the default Apple 'moving the document' setting is extremely consistent with the rest of the trackpad. When you use one finger you move the cursor, not the viewport relative to the cursor. Why would it be different with two fingers?
Traditional scrolling is consistent with the arrow keys, that is, moving your fingers down on the scroll wheel or the trackpad moves in the same direction as pressing the down arrow in the keyboard. (The arrow keys traditionally move a text cursor through the document, and the scrolling happens when it hits an edge; this is why they content scrolls in the opposite direction.)
For the same reason that controllers have both "normal" and "inverted". It's all in your point of view. Are you controlling like a mouse (up on the joystick looks up) or like a joystick (forward on the joystick is like tilting your head forward, and looks down).
For me, I hate the "natural" scrolling, because I map scrolling motions to "up" and "down". Moving my fingers downward should do what I think of as "down", which is to see what's below my current screen. I have an XPS 15 with the touchscreen, and only when you're actually touching the screen does "down moves the document down (and goes up toward the top)" make sense.
Either way, one method is "the original one", the other method is the opposite, or reversed, from the original method.