It in no way illustrates that, for the reasons programminggeek provided.
Google+ is making a huge splash, that is about the only meaningful statement that this graph illustrates. It doesn't suggest that they could dethrone facebook because there's a hell of a lot more to making a good social network than how quickly it gets ten million users.
For me and my friends, google+ is a dead zone. I signed up to check it out, and barely have looked at it since. I would like to use it some day, when more of the people I really want to connect with are on it, but there's really no certainty that it will make it to that point.
The graph provocatively illustrates that google+ could steamroll over facebook in a very short time, if they play their game right.