The author fails to understand that fungibility is tangential at best to anonymity.
fungibility is based on the equality of a unit of stuff. short selling works with fungibility, you hire some shares of IBM. Once you have them you sell them, when the price drops you buy them back. The hire period ends and you return the same number of shares, but not the same shares. This works because it is agreed that shares of the same time in a company are all agreed to have the same value.
but, this principle works with anything that has uniformity of price. This is determined by the trading environment, and not the thing being traded. Stocks nominally have unique IDs, at least for accounting purposes (otherwise how do you stop unauthorised re-issuing, and distribute dividends)
Gold is fungible, as pointed out, but anonymous gold is worth less than gold with provenance. To prove that gold hasn't been messed with is expensive, so keeping accurate and verifiable chains of custody is required for fast trade of gold.
Sure one can melt down gold and make it anonymous, but thats expensive. You can barter with your local drug lord using physical gold bullion, but you'll need to be damn sure its verifiably pure, so you'd better hope the serial number and foundry stamped on the front checks out.
Its far quicker to just transfer the ownership of bullion in a known vault, and that has certain guarantees about custody, purity and security of product.
In short, the author fundamentally fails to understand basic commerce, let alone post enlightenment stock markets.