Yes this is true. However that's better than anyone else has done with Anderson since his entrance into the UFC. Again, I'm not saying that I think that Sonnen is going to win this fight, all I'm saying is that stylistically he presents a problem for Silva and matches up with Silva the best out of anyone in the division.
On the feet nobody in that division is going to beat Anderson, nobody. And, since his fight with Travis Lutter he has really seemed to improve his takedown defense. Neither Thales Leites, nor Demian Maia (who may have both had a chance of submitting Anderson on the ground) could get the fight where they needed it to be due to a lack of takedown skills.
In fact, only Sonnen has been able to consistently and repeatedly take Silva down to where he is at least potentially beatable. That in itself says to me that he at least has a legitimate chance of grinding out a victory and ending Silva's unbeaten reign at MW.
But like I said, if his fight with Bisping is any indication of where he's currently at as a fighter (following his suspension), then I think Anderson should beat him again.