Yes, it's very easy to come away from a casual reading about Erlang and have the impression that it automatically makes your code work across server clusters. I did myself the first time. Some of that is perhaps overexcited advocacy, but some of it is also that when reading about Erlang for the first time you don't quite know what all the terminology is so it's easy to be a bit off.
Erlang does have some tools that make it legitimately easier to write cluster-aware software, such as the message-passing operator not caring about what node the target is on, and transparently handling all network communication from serializing the Erlang term on one side and deserializing it on the other. Erlang's terms, the basic data types, are designed for exactly this use case, and as such a first-class concern, they are good at that particular use case.
However it's still easy to accidentally write some code that will only run on a single node and you still need to be aware of what you're doing to be sure you don't accidentally wire in a hard-coded dependency on being in a single OS process. But when you contrast that to the default state of most other programming languages, which is that they have essentially no concept of cluster communication at all, you can still see how this is an advantage over those other languages.
