Did the mechanic install the wrong timing belt?

[wuwei37405]

I recently had the timing belt replaced on my 2005 Aveo by a professional mechanic. About a 1,000 miles later, I changed the valve cover gasket myself. It was then that I noticed the installed timing belt was not as wide as the camshaft pulleys. Should I be worried? I am going back to ask the mechanic ""why" but he could tell me just about anything because I am not an expert. I will try to upload a photo to show what I mean.