You're right. It is responsive and not exactly elastic. But even without changing your browser's width and just zooming in, the layout goes from 3 columns to 1 column and doesn't just make everything bigger. So you could say it is elastic too in some way.

I used to experiment in elastic designs (using em for all widths) but it was clearly difficult to maintain. But the main reason why I quit doing it is because nowadays most browsers' zoom in function isn't only increasing the font size but increasing all widths accordingly too. It's a complete zoom rather than a simple font increase.