OMG Mod Meltdown! Was it the chicken or the eggs?

My good friend that introduced me to vaping in 2014 texted me this morning with some scary news.
She was rudely awakened at 4 a.m. by a huge cloud of noxious smoke, and as she tried to get fully awake she grabbed her Eleaf iStick 100 watt TC mod from her nightstand for an awakening puff. She dropped her mod instantly with a scream of pain and surprise! It was the source of the choking smoke! Thankfully with the aid of some household implements, her husband managed to navigate the super hot sizzling leaking batteries out of the mod and into the cat litter bin. Her nightstand is scorched and blackened in a mod bottom shape, and her hand is O.K. thanks to her superfast reaction! Her iStick is toast.

 She did not have this plugged into any pass through usb charger, and her husband ordered the batteries online. She had this device for only a few months. My friends have a state of the art smart battery charger and she had just put the relatively new and fully charged batteries into her mod the previous evening before going to bed. She left her device on and on her nightstand as always. I'm vaping away on my little Eleaf iPower a bit nervously as I write this. I also have an old and still great Eleaf 20 watt that I use when my iPower needs a charge up. I have an Eleaf 40 watt TC that I retired because I became suspicious of it after I accidently dropped it and cracked the display. It seemed to be getting hot when it was charging, and I got way too paranoid to continue using it. What is to blame for this minor scorching that could have been a really bad accident? Is it a fault in the iStick 100 watt TC or is it the batteries themselves? Could the smart charger be to blame? I know that my friend and her husband always buy the best quality products. Could he have been duped by knock off batteries? Could this be a faulty iStick? Faulty iSticks have been known to occasionally happen and knock off batteries have been known to be sold in disguise. The search for answers continues. In the meantime, my friend is vaping with her Kanger products and here is what Battery University has to say about battery disasters: http://batteryuniversity.com/learn/article/safety_concerns_with_li_ion