Very often ZIP code is used as alias for postal code even in international context. I see "zip code" more often than "postal code" on international address forms.
I'm not saying they don't exist, but I'm not sure I've ever seen one.
The US-based organizations using the term "zip code" for non-US addresses are doing so either out of ignorance or expediency, since fitting "zip/postal code" into a space is sometimes not possible.
That doesn't make it correct, and I don't believe that some peoples unequivocally wrong usage of a term should oblige other people to qualify their correct and unambiguous usage of it.
As a recent example, see KanbanFlow for example https://sites.fastspring.com/kanbanflow/order/customer
The "Zip code" input field is simply hard coded for every country.