You only had to install a free app. You didn't have to buy a Moto X phone (50 GB for 2 years), a regular Chromebook (100 GB for 2 years) or a Chromebook Pixel (1 TB for 3 years). Google Drive's offers for phones and Chromebooks have special pages.
It's funny to see that Google offered free storage for installing an app that used to cost $15-20.