Leaves burning out on the water?
The article didn’t indicate that the burning was in the water.
If it was, then you would have to wonder how it could be the engine, which certainly would have been at the bottom, not on the surface.
And the engine wouldn’t have had enough fuel “self-contained” to leave a slick that would be burning a half hour later, would it?
Maybe I misunderstood the entire article. :-)