Yes, But they tested Yahoo of all websites to make sure they don't send tracking data, and not an unrelated website like wikipedia or archive.org. The only non-google test case too I might add.
There's no smoking gun here, but I don't think that concern might be dismissed out of hand. It might be good to see what Yahoo's take on this. This could even evolve into participation by the US Attorney General. I'd like to know more, either way. Like if Yahoo was independently added to the list at a later date, or if it was there from the start?