This site suggests that a large release of methane gas could cause fireballs...
(info is about 1/3 of the way on the page.)
So, while rare, it seems not impossible that the gas might have caused this fireball, as when the plates shift with earthquakes, some gas may have been released, causing the fireball.
In any cause, I'm sure glad I don't live in NE!
http://www.volcano.si.edu/world/vol_...20of%20Marmara