Hasta La Motion!

Hi!
I am wondering if anyone here knows how ILM made their z-comp in this video: http://www.youtube.com/watch?v=kIfHZ5ErMiw
More exactly the nodes that are in the yeallowish-brownish backdrop at 7:25 in the video.

From what I can see they are not using any ZMerge node and he is talking about "cutting it out with the z-channel" (2:25 in the video).

I know the video is low-res and there is a higher-res one at fxguidetv but not so high that you can figure out what nodes he’s using and he never shows any settings of the nodes.

I know a lot about integrating Nukes 3D-system with renders and position-passes and I got it working with the standard ZMerge and I know how to cut out stuff with the z-channel.

I just want to know if someone knows if ILM are using any special tricks in that setup to deal with aliasing and mblur issues and they seem to have a nice color bleed around the explosions also.

Thanks!