The conclusion of this research seems to be an example of confusion between correlation and causality.
Another explanation to the conclusion of this research (although I didn't red the article): the brain processes involved for solving the maths problems of the experiment could imply some "higher level" brain activity which is also needed for the brain processes involved in the solving of the language problems of the experiment, the two (language and maths circuitry) working completely differently. An image: it is not because you need electricity to grind your coffee and to prepare your bathwater that the electric boiler works as a coffee grinder.
So the argument is not convincing. But although the argument is weak, it's still possible anyway that math and language brain processes share important common characteristics! More research is needed!