That comment about gold bothered me so I looked it up.
Gold
- Density: 19.283 g/cm3
- Atmoic Weight: 196.966
Mercury
- Density: 13.546 g/cm3
- Atmoic Weight: 200.592
So, while a mercury atom is heavier than a gold atom, objects made of mercury tend to be lighter than objects made of gold (unless we're in very specific and contrived circumstances).
Why did the god say this? Either it's a misunderstanding (by the author or the character) or it's a clue about how god powers work.
What could the clue be hinting at? No idea. Haven't reached the level of nerd needed to explain how mercury could be heavier than gold.