In addition to @hadriens good answer (+1):
(i) Many forms of rock appear to have a density of about 3g/cm^3 (see e.g. here), so a density of about 3.3 g/cm^3 certainly does not imply that the moon is hollow, it could simply be made of solid rock. I would suggest that the Earth is more dense because, unlike the moon, it has an iron core (iron has a density of about 7.8 g.cm^3).
(ii) The moon is not perfectly round, its polar radius is 1736.0 km, but its equitiorial radius is about 1738.1km. It is more closely spherical than the Earth, but that isn't surprising as its rotational period is about 27 days, which is much slower than that of the Earth, so the centrifugal force is lower (although so is the gravitational force, which would make it easier for the moon to become more oblate). The flattening of the Earth is 0.0033528 and that of the moon is 0.0012, so the Earth is three times more oblate than the moon, but then again it is spinning nearly thirty times faster.
(iii) Apparently, some very large craters have convex floors, simply because the convexity follows the curvature of the moon, so unless some clarification is provided, this argument may simply be a misunderstanding.
(iv) This is a non-sequitur from (i) to (iii) as none of those actually imply that the moon is necessarily hollow or artificial. (i) and (ii) are very weak arguments, as very basic fact checking shows that there is nothing unduly suprising in either of these "facts".