There was a more detailed account floating around. Essentially, each battery cell is in its own fire-resistant compartment. The fire crew that responded to the call used procedures that are standard for other electric cars, but are not proper for a Tesla. Essentially, they "punched through" these compartments in an attempt to extinguish the fire, which actually exacerbated the problem by allowing the fire to spread to other battery cells.

When the fire department arrived, they observed standard procedure, which was to gain access to the source of the fire by puncturing holes in the top of the battery's protective metal plate and applying water. For the Model S lithium-ion battery, it was correct to apply water (vs. dry chemical extinguisher), but not to puncture the metal firewall, as the newly created holes allowed the flames to then vent upwards into the front trunk section of the Model S. Nonetheless, a combination of water followed by dry chemical extinguisher quickly brought the fire to an end.

http://www.teslamotors.com/blog/model-s-fire

I saw a Nissan in fire a month or so ago outside of Philly. Car fires happen regardless of engine technology.