You should scroll down a bit more. The mosaic example is not the example for an animated gif. You should use the one that says 'Create animated gif.'. For your case this means that you have to add an image for each frame to a MagickImageCollection. The following will show you what the person that created the SmallFullColourGIF.gif had to add to the collection to create that image:
// Load Imageusing (MagickImageCollection images = new MagickImageCollection(@"C:\SmallFullColourGIF.gif")) { // collection.Optimize will create frames with only the difference this method makes sure each// frame is a complete image instead of just the changes between each frame images.Coalesce(); int i = 0; // Save each frame to a fileforeach (MagickImage image in images) { image.Write(@"D:\SmallFullColourGIF-" + (i++) + ".gif"); } }