No, a point does not have a length. A point is only a location - it has no extent in any direction.
You are correct in guessing that the function
vSize() returns the distance from the origin to the point. The other function,
vSize2() returns the square of that distance. This is used in calculating the distance, and in some cases it may be useful to work directly with the square of the distance instead of the distance. This avoids calculating square roots, so can lead to improvements in speed and accuracy.
Note that as Nero points out, the functions are using only
ints (integer variables and return values). The distance between a point and the origin is not in general an integer value, even if the coordinates of the point are all integers. The distance squared returned by
vSize2() will be accurate, but the distance itself returned by
vSize() will be accurate only to the nearest integer.