Other tricks were done to make sure it looked like a huge crowd. Notice that the background was removed and the crowd blurred for effect.
A professional photograph is not blurred unless the photographer wanted it that way.
Also notice, that when there is some non-left-wing demonstration, the photo is taken from far away and you see the crowd from a great distance - thereby making it look smaller.
Photoshop is not necessary to make a crowd look small or large.
I'm not so sure about that, I've try to take long distance pictures with my cheap camera and I can tell you it is really hard to get the right exact focus with a big telephoto lens. Also you would be amazed at the heat waves that a camera may catch off the pavement even on a cold day.
I don't know the picture may be doctored on purpose, but it is really hard to tell on some picture taken off of some web site that has probably been compressed considerably from the original to fit the web space etc.
I assume the picture was taken with a digital SLR or something like that and if they put the original picture on a web space you would have to scroll up and down and left and right all day just to see the picture. When compressed down to size for the web space a lot of the pixels are probably eliminated thus making it look like it was doctored.