Hmm. So knowing the mod has a 10 second shut off, and the atty itself didn't have a short in the build, assuming you are correct about no tears in the battery wraps...
Crack open the mod if possible and inspect the 510 pin. Perhaps, the positive pin dropped down and shorted on the negative lead or the case from the atty wiggling around in your pocket. Which points us to another issue, even if this was what happened, the short protection should have tripped on the mod, preventing the continuous venting, but it seems for some reason, that short protection failed. Now this is just a guess, based on everything else in this thread. And, something similar happened to my istick 100w, except it didnt vent, the + lead fell off the 510 thread and shorted with the - lead. Short prevention popped and stopped the batteries from venting..
Now this is just a theory of course, since i can't take the mod apart to inspect, but seems more likely than your batteries just fulfilling a suicide pact and venting themselves. LOL.
Certainly though, contact the manufacturer with details and let them know what happened.