I think the author's use of the microservices is unfortunate and confusing.

With the BEAM, it is easy to create fully independent process trees. The architecture enables it. In fact, you can pull in dependencies and add them as "OTP applications" (which is in essence a fully independent process tree, doing its thing.)

The BEAM lends itself very well to structuring parts of your application as independently supervised process trees.

This is similar to microservices, where each microservice represents a fully independent process tree, with which you can only communicate via well-defined interfaces.

As I said, the author's comparison to Microservices is very unfortunate.