I Googled zcash and fungibility, found this one article from @dnaleor on Steemit. Assuming that's the one you meant, the article was saying that in a cryptocurrency world where every transaction is globally visible, privacy is important for fungibility.
Let's say you're running an organization which is being censored by the government and you're paying admins in BTC. Everything is public, so anybody can see which addresses are performing transactions. If the government found out which address belonged to you, they would then be able to track all the coins that flowed through your account, even when the people you paid tried to use them elsewhere. Essentially, they could mark your coins as "dirty" money which is a criminal offense to own.
On the other hand, let's say you paid admins in fungible fiat cash. When your admins go to buy food with that cash, there's basically no way to know where that specific dollar bill came from. Any $20 bill is interchangeable, whereas you can uniquely identify "one bitcoin" by all the transactions it was involved in.
So long as transactions are publicly tied to identifiable addresses, you can't get real fungibility -- privacy really is a part of the equation.