I suppose that's possible, although this could be pretty easily ruled in or out by any competent geologist. It would require a shallow high pressure reservoir (unlikely right there) which is suddenly fractured (presumably by earthquake) with an enormous release to the surface of a couple hundred billion cubic feet of methane.
Presumably there is a campfire or other ignition source in the immediate vicinity.
The odds of this being the culprit behind Tunguska are very remote.