But too lazy do to the arithmetic:
There might be a tiny bit of truth to the flat earth statement though.
Even if the fps is too low for escape velocity the fired bullet will travel a bit while the dropped bullet drops. The fired bullet will accelerate downward and drop at the same rate as the dropped bullet.
However, on an ideal spherical billiard ball earth the earth will have dropped away (relatively speaking) because of it's curvature.
Without doing the arithmetic I suspect that even under ideal conditions the difference will be too small to measure. On a real non billiard ball earth the local non-sphericalness will mean that the orginal statment about both fired and dropped bullet being equal is correct.
Of course, you'd still have to be firing on a several kilometer long mirror smooth fireing range for it to work out.