I agree the title is misleading, but in both directions. The 40% number is just for Marcellus shale gas wells - that is, basically shale from primarily a single state (Pennsylvania).

Also, I would think that the fact that it just comes from shale gas well wastewater means it would be more commercially viable to actually extract.

Since this is high up, I'd like to point out some comments made down thread that cite the paper disagreeing: the Marcellus well water isn't very economically friendly at all. For many, the composition is off (e.g. too much mercury) and for most, they produce most of their water for the first two years of operation.

https://news.ycombinator.com/item?id=40375251