According to a Reddit poster, an LG G3 belonging to her little sister exploded in bed while it was recharging. Normally when we hear a story like this, we immediately blame a third-party charger or battery. In this case, everything about the phone was supposedly stock. In other words, the device was using the original battery and charger that LG supplied with the handset. The phone was not placed under the sheets or the blanket, and was just lying on top of the bed while plugged into the charger.
The fire caused the destruction of the mattress, which was tossed out the window when the LG G3 continued to burn is way through the material. The phone was used just a minute before the fire started, and the user did not notice anything unusual about the device, which was not even warm.
A series of pictures can be viewed by clicking on the source link below. There is a photo that was taken while the phone was burning through the mattress, and other images show what the battery looked like after the fire. Basically, it resembled a large lump of coal. The casing of the LG G3 is burnt and obviously was melted.
Assuming that the story is legit and no third-party equipment was employed, this does seem to be a fluke occurrence.