> That's the Smalltalk school of OOP

In particular the "Smalltalk-72 school" which had indeed something like "message passing" (though still synchronously). Starting from Smalltalk-76, and particularly in Smalltalk-80, which is the Smalltalk we know today, the object model pretty much corresponds to Simula-67, with compiled methods dipatched via virtual method tables. The only difference is, that in Smalltalk, the dispatch goes via the internalized string address of the selector (vs. method index as e.g. in Simula-67, C++ or Java). See e.g. https://dl.acm.org/doi/10.1145/3386335.