The rim itself is a fairly low-budget OEM Weinmann with no eyelets but three chambers -- basically, a quasi-Deep V exterior shape with a couple tunnels thrown in for added girth and (one would assume) strength. It popped right at the seam, which was (as near as I can figure) behind and above the tire's contact patch, perpendicular to the impact, and right in the worst of the blast zone.
I assume from what little I know of rim construction that this is what's called a "pinned" rim, since there's certainly no sign of a weld here. That wiry looking bit spanning the gap (and barely holding the rim together) is a metal pin with spiral grooves running in opposite directions away from the centerline. My guess is that the pin plus some sort of industrial sticky stuff plus a lot of pressure holds the rim together, at least until some idiot hits it from the side.
(Aside: What you can't see is the big rim decal on the reverse, still valiantly holding across the chasm of failed rim. The moral of the story, kids, is that big, ugly brand labels are actually supposed to be a safety feature.)
There was also an interesting failure mode away from all the excitement:
I dearly hope no one takes this as a shot at Weinmann or their products. Remember, this rim took a pretty nasty lateral smack, the sort of thing that would put just about any hoop in the recycling bin. Even if the joint had been welded, I suspect the force would have potato-chipped it past the point of re-true-ability.