I can't quite follow what the article is trying to describe because of the heavy use of analogies.

A Google search makes it look like Julia has a mechanism where you can extent the sets of overloads of a function or method outside the original module. The terminology is different (functions have methods instead of overloads in their speak). I don't see how that feature solves the problem in practice.

Julia multiple dispatch allows dynamic polymorphism.

Check https://stackoverflow.com/questions/1801216/what-is-the-diff... and https://www.youtube.com/watch?v=kc9HwsxE1OY