I have seen charts like those elsewhere. Always of course they show some monetary metric such as the aggregate money supply, or global public debt, or some other such metric, with the implication being that there is a causal link between the two.
But hey, for a laugh, why not overlay the price of gold with global coffee consumption, or the number of McDonald outlets in Asia, the number of Krispy Kreme donuts consumed worldwide or the total number of computing devices in the world. I imagine the results would be quite similar.