You can manipulate it so that gold is more valuable by hoarding it, but that doesn't really harm the economy (save to the extent that the government has high taxes in order to gather their hoard of gold). You can't manipulate it such that there is more gold than there actually is, or at least, not normally. The US had some success in doing this up until 1971. If you use circulating gold coins, then there is no way to manipulate the price down. All you can do is restrict supply, which makes those who are holding gold richer (which I think is what that quote was referring to).
However, that was really only the case with mercantilist economies. In a free economy, even that type of manipulation is difficult. When people hoard gold, they don't get any real economic benefit, unless they create their hoard when there was a lot of gold, and spend it when there is little, in which case it's a good thing because that creates a speculative market which would help to regulate the price of gold. If there is only one hoard, the owner of the hoard gets no benefit, because each piece of gold he draws out of the economy is more expensive than the last, while each piece he spends, buys less than the last--it ends up being a zero sum game. By collaborating with rich people, it could enrich a few at the expense of the many, though that expense is the result of the taxation required to create the hoard rather than the change in the value of gold (which on the whole is always neutral, all other things being even).
The only way I could see a benefit would be for an entity to hoard gold and wait for a large increase in population, which would mean that the supply of gold per person has gone down, meaning they can purchase more labor with it than they could have had they spent it right away, but that is just one of the benefits of saving. The only real crime is the taxation.
