He's basically saying that if you create a popup small enough width-wise, then you can hide everything before the # so that unless the user actually goes into the address bar and scrolls left, all they will see is what you put after the #. Here's a screenshot so you can see what he's talking about: http://lh6.google.com/mikediaz.360/R_PpsHN-hCI/AAAAAAAAABc/_F2JZMpUiS4/Screenshot.png
