Joe himself once said on stage (it was a video with him and Kay on stage, not sure of the name), that Erlang is either the most OOP lang or the least. I think he meant, that it depends on what OOP you look at. If you look at Smalltalk and message passing, as Kay highlights as the prominent ideas, then it might be the most OOP (or somewhere close to), while it is a 180 from mainstream OOP, when we look at the actor system and how distributed systems work.