Edit: Turns out the Dutch are the third biggest consumers of milk per capita in the world[0], looking at the list of "tallest" countries on wikipedia[1], there seems to be a great deal of overlap at the top of the two lists. I wonder if a secondary factor could also be related to vitamin D exposure, but I couldn't find a data source for that.
0. https://en.wikipedia.org/wiki/List_of_countries_by_milk_cons...
1. https://en.wikipedia.org/wiki/Template:Average_height_around...