The point of the paper was:

"Scientists have mapped Earth's electrical conductivity on a global-scale in 3-D for the first time." I think the graphic was the electrical conductivity map, although they I believe one of the points of the paper was there was some level of correlation with subduction zones.

They say it "coincides with subduction zones" implying a correlation. They draw no conclusions in this summary paper, speak about the various theories talking about water below the mantle.

"There is some evidence that there is many times more water below the ocean floor than there is in all the oceans of the world combined. Our results may shed some light on this question." ...

"Ultimately, the scientists hope to produce a model quantifying how much water may be in the mantle, locked up in its rocks."
-----------

My interpretation of the paper was that by having more complete and detailed studies of electrical conductivity, the could potentially incorporate that information into more complete models and refine their theories of earth's water cycle. Sounded like they had a long way to go and this was just a baby step with the usage of different data to complement seismic sounding. Peppered with "may", If you can find any hard statement in this paper, I'll give you a nickel.