I don’t know what they think, but in my opinion it’s total BS.
You would have more fumes coming off a freshly laid asphalt road than you would have coming off of the oil that is washing up after having been baking in the sun for weeks.
Then, also, there's some talk that the BP oil rig had hit a huge reservoir of methane, and/OR that as sea life dies from the oil that the decomposition creates high levels of methane.
Some reports state that levels of methane are ONE MILLION TIMES higher than normal.
I have NO idea as to the veracity of this.