Earlier quoted context omitted.
He did tho. He mentioned more than once that OOP was more about message passing than behavior + state.
Yes, that’s what I mean by vague suggestions. How do you actually build and maintain a system of any complexity with that? How do you ensure it will do what it is supposed to do? And Smalltalk wasn’t that, it is mostly just regular method calls and not “message passing”.
Reminds me of the RESTful guy, Roy Fielding (though I respect and like Alan Kay way more). If you've read any of his online interactions, apparently nobody does REST like he envisioned. It simply doesn't exist in the wild. When asked about some REST API, he'll claim it's not RESTful, it's wrong, that's not what he meant, etc. "But what would be right?", you ask, and he'll reply "Read my paper! HATEOAS! (Hypermedia as the engine of application state)". "Ok, but what does it mean in practice, how do I go about building an API with HATEOAS?"...
...and there's no answer for that besides "read my dissertation". He can only tell you what you're doing wrong, but nobody has been able to build a "true" RESTful API to Roy Fielding's satisfaction.