Looks like an overlapping mesh at first glance. Have you checked for that? (Edit mode, select all, W --> Remove Doubles) (If that doesn’t do anything, then hover the mouse over the troublesome section, deselect all (‘A’) and then press L then G to drag the selected mesh around – look to see if there’s another mesh under it.)
I think so too, but it doesn’t have to necessarily be in Edit Mode, he could have just duplicated the mesh accidentally, and left it at the same position, and it’s overlapping… After you’ve tried “Remove Doubles”, try deleting the mesh once and if it’s still there, then that should fix your problem (you may have multiple duplicates, if after deleting the render still seems distorted, try deleting it until you don’t see anything and then just undo the last step - CTRL+Z)
And if it is duplicated then all points are in the same place and remove doubles would quickly remedy the problem. Most of the time this type of thing is created during editing. A quick way to see if the object is duplicated is to simply look in the outliner, while selecting in the viewport can be problematic when dealing with overlapping geometry.