Every once in a while a science story comes along where one's first reaction is "That's BS!"...but after thinking about it, one realizes it makes sense.
After all, dirt absorbs water like a sponge, a volcano is a mountain-sized sponge (if only for the first foot or so of dirt), and in this case, there's thick vegetation keeping the saturated dirt in place.
And any wet sponge several square miles in size is pretty doggone heavy.
So...yeah - this makes sense. My only question is whether this phenomenon is more likely to occur with shield volcanoes due to the sheer breadth and relatively shallow grade of their slopes, as opposed to cinder cones or composite volcanoes where the steeper slopes would allow for more efficient runoff of rainwater.