Yes, for all observers. It is not a statement that the speed of light has always been the same. This article's statements about Einstein are wrong.
Would also mention that Stephen Hawking, I believe, said Einstein did not prove Newton wrong, merely incomplete. Seems to me that even if this speculative theory is proven correct, the same would be true of this discovery.
Also, you are correct in your statement that Einstein qualified by saying "for all observers."
Since I don't really have a science background, I've really never understood the controversy over light changing speed. I thought that prisms and water proved that light changed speed, or at least strongly suggested it, as a change in direction required a change in speed.