Any pedal will unclip if you apply enough twist in your sprint, it's pretty common to do this unconciously especially if you're going from a standing start. It's possible you had a worn cleat too. In any case sorry to hear about the mishap and heal up.

If you like the Speedplay cleats and feel (I don't, but that's just me) you'd have to actually snap the spring wire to get a release if you kept the pedal straight. Virtually all the other pedals out there could potentially release with enough up force, I've pulled out of my Looks doing standing starts at the track (now I use straps mated to Euxstars). That said that's the only time I've had that happen; I've done a ton of race sprints on them with no issues, I do keep the tension adjusted pretty tight, and I do keep the cleats refreshed when they show wear (I've broken a few of the early versions).

With any cleat or pedal you need to keep an eye on wear.

Downside to the Speedplays is they have a pretty small platform and the cleats are easily clogged up with dirt.