The OSI model can be used for LAN and WAN networks, allowing the interconnection of [vendor] closed systems and it only informs what each layer have to do.
Someone said that this phrase is false, because OSI (Open Systems Interconnection) model, "as the name says", only allows the connection of "open systems".
So I'm wondering if there is any vendor closed network that, nonetheless, can communicate with another network using as the middle man an OSI based network. As I see it, in the broad sense of the phrase, two closed systems don't need to be directly connected to be interconnected, they can use a middle man.
Searching I only found about closed systems in the sense that they can't be freely joined.
Is that phrase true or false?