Alan Kay has had many opportunities to specify precisely what he means by objects and messages, and based on reading his more recent (or less old) VRI papers, Kay draws inspiration for objects from biology, where swarms of molecules pattern match against the partially constructed molecule and build it up step by step. I've seen him give an example in only one paper.
Needless to say this is not how Smalltalk works.
I've always gotten the strangest feeling that Mr. Kay made up the distinction between Smalltalk and later OOP languages after the fact. I think this is precisely the reason I get that feeling: because despite what Mr. Kay says about Smalltalk and OO, programming in Smalltalk feels very much like programming in any other OO language.
I don't mean any disrespect to Mr. Kay. I give him the benefit of the doubt in assuming that his intended language was different from the language that actually materialized, likely due to implementation issues. In that regard, as a language designer I can very much sympathize.