The only thing I can think of is that you stripped the threads. Since the cleat was screwed into a separate plate, then I'd think the only thing you could have stripped would be the threads in the screw holes on that plate. (BTW if you damage the ones in your shoes, they are likely replaceable). Unless you had some kind of impact to a non-replaceable part of the shoe (such as breaking a carbon sole), then the shoes should be fine.

I'm the most concerned with why your cleat didn't release before being ripped off the plate. It's not that uncommon to break a composite cleat with the right kind of fall, but I've never seen Speedplays do what yours did.