I'm guessing he means that you could have split the background Image into a body class with a background color, the Logo could have been also its separate class with a much smaller image, then the frame itself could have been split into 3 separate images (top, center, and bottom) and finally the boxes where the counters are could have been 1 small image that you could apply 4 times rather than have all 4 boxes in one image.
The text also could have been created with css rather than using an image but overall it is still a really well designed page.
If you did all this the load out time would be much faster than having large images.