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I think he's saying that most OOP languages have single dispatch, while multiple dispatch is more like the real world.

https://en.wikipedia.org/wiki/Multiple_dispatch

This is well explained here: http://c2.com/cgi/wiki?ObjectOrientationIsaHoax

I think the first interpretation is that he thinks a language should have either traits, multiple inheritance (of implementation) or mixins.

The second interpretation would be that a language should have algebraic data types.

My guess is that in OO you are typically only parameterising `this`, and therefore only talking about one facet of the domain. Family polymorphism (or virtual classes) provide a way around this...