it's not as mysterious as it sounds. every data structure (including modules and anonymous functions) has a binary serialization and every erlang vm is also an rpc server that can receive arbitrary data -- including whole programs -- and execute them. your vm of course needs to know about the remote vms to do so but that's where the rudimentary clustering mechanism in erlang comes into play

Also no shared memory in processes and they all communicate strictly through message passing, so running a piece of code in the local node, in another node in the same machine or in a node on the other side of the planet is a matter of telling which pid you want to send the message to, the BEAM will figure out how to send the message to the correct place in the cluster and your program will be none the wiser.

You can find all the details about Erlang internals in The BEAM book : https://blog.stenmans.org/theBeamBook/

It's basically a distributed RPC system. Your call is a message.