I'm not sure the method he used. It appears there is more than 1 way to skin a cat after all (though why you would want to skin one I'll never know!)

But, in gimp you can create a grid on a new layer. When setting it up, either remove the verticle or horizantal, change spacing and line width/color to your preference. Go to your outline, shrink it or expand it (depending on if you're going for an internal or external "highlight") and create boarder (again to your width preference). Go to your grided (which actually should be a whole mess of parrallell lines), and hit delete... er. Should have just removed everything not in the selected boarder area. Unselect, and filter as you prefer - blur, fuzzie, motion etc to get the effect you want.

If you want them in a diagonal rather than verticle or horizantal - before deleting the unselected part - just rotate the parallell line layer to the angle you want - then hit delete.

If that makes any kind of sense? (I'm not at my computer w/ gimp on it.. so my terms may not make quite as much sense - and I may be calling them what I think they are rather than the actual button names).

Granted, there is probably a lot of other ways, maybe some that are even simpler (scripts or what not). But, I don't really use any scripts. Just the basics.