From purely a mechanical engineering math exercise the "Center of the World's Land Mass" should be a spot where the square miles of surface area was equivalent in all 4 segments.

By eye the NE quadrant (30 degrees-210 degrees) would have far more land mass than the SE quadrant (including Australia).

If he was talking about total surface including water then any equally divided quadrants would add up to equal.

I would say "Mythbuster busted".

Jammer