Re: God this episode was crap
" If the creature stayed within the bounds of the moon then the centre of gravity would also stay within the moon."
So in your view, if you were to glue a metal ball bearing inside the surface of a beach ball then that beach ball wouldn't be unbalanced? You are right in that the centre of gravity is important, you just don't understand that if one part of an object is more dense than another it does move the centre of gravity and hence alter the gravitational effect. This is apparent on the earth where some parts of the crust are thicker or more dense and hence the acceleration due to gravity is different depending on where you are.
"Except the moon hadn't been putting on mass over time it had suddenly put on mass since the gravitational effect on earth was a rapid change rather than something people had had time to adapt to over millenia."
It was only a suggestion for one possibility, perhaps the moon had been accumulating the energy over its lifetime (4.5 billion years) and only started converting it to matter recently, or maybe the rate of matter generation had increased, or maybe it got the energy/matter from another dimension? My point is that only stupid people dismiss things as impossible without even considering any of the infinite number of possibilities.