"All about message passing" was Alan Kay's vision of OOP, which was very distinct from what is considered OOP both before and after. He did coin the term "OOP"

"All about message passing" was Alan Kay's vision of OOP, which was very distinct from what is considered OOP both before and after. He did coin the term "OOP" himself, though, so of course his definition carries a lot of weight, of course. Even Simula, the original OOP language, is much closer to the procedural-ish OOP than to Smalltalk.