Google gets copyright over any code contributed during the duration of your employment - that's what happened in the project you link to. If he doesn't touch it while working at Google, there is no such code. You're supposed to disclaim any open-source projects you wrote before Google employment - I did, and then didn't work on them while employed.

It is somewhat debatable whether this provision would stand up in court, but do you really want to fight a court battle with Google's legal team?