I wouldn't worry about methane combusting in an anoxic environment like a mile undersea, either. Ahem. But the clathrates have a spongy yet brittle structure that traps methane under pressure, and it's been known to be explosively released. I'm speculating that they drilled into a pocket, got a methane blowout up the pipe, and that's what exploded when it reached the rig, and oxygen.

There's been some overblown speculation about it, like the John Barnes novel based on collapse of massive banks of the stuff from Alaska down to South America. But in moderate quantities, localized, it can still do some damage. Like taking out a drilling rig?

And further, if there's a large pocket under or near the explosion, could it have cracked and be leaking, with methane pushing out crude?

The Gulf has known pockets of methane clathrate, as do most of the continental shelves. The interesting question is their location and extent.

All of this is just sheer speculation, and I wouldn't be surprised if a resident geologist patiently explained the exact degree to which I'm full of the brown-that-is-crude-but-not-oil.