He used the Simple Native Trainer mod. In my opinion, GTA IV has the best Simple Native Trainer mod. GTA V doesn't have such a comprehensive Simple Native Trainer mod as GTA IV.
Exactly, that's why I put the two in a vacuum (space) The only thing related to the speed of an object is it's air RESISTANCE. Go and grab an ordinary pen on your computer desk, I'll wait. Find one? Ok now go and grab something heavier ( like a basketball, again I'll wait) Ok good, now go take those two over any flat surface at an equal height and drop them at the same time. If the basketball fell faster then you are a magical wizard. (Coming from an undecided major with some common sense)
Now did i say they were in space? No i believe i said you do it, and if you want to use a bowling ball go ahead, they will still fall at the same speed. As i said, the only other thing related to it besides the force of the gravitational pull of the objects is AIR RESISTANCE, a feather would fall slower because the AIR around it decreases the force of it's gravitational pull, unlike a bowling ball which is much more aerodynamic in comparison to the feather.