I don’t really know, and I’m not a lawyer. But really, when you link to a font hosted on Google, you are just using Google to display the font. You aren’t actually giving the font away to anyone as such, as its source is still hidden. So the licensing arrangements really affect Google rather than you. That’s how I understand it, anyhow. The font has been licensed to Google—by the font creator—so that people can display it on their sites.
All of the fonts are Open Source. This means that you are free to share your favorites with friends and colleagues. You can even customize them for your own use, or collaborate with the original designer to improve them. And you can use them in every way you want, privately or commercially — in print, on your computer, or in your websites.