I don't think that it does to be honest. I think author does not understand typography, he did some Googling and tinkering with font software and that's about it.
The real story is more complicated. Yes there is no 'em size' as a physical constraint in digital world. Yet the concept that the 'em size' represents is very important for a font. Font is more than the collection of glyphs (shapes of letters). Things like em size and default line height may seem arbitrary but they are important decisions made by font designer that should be respected by users of the font.
