Looks like there is a mistake in the article. The new plane will "burn 70 percent less fuel than a Boeing 737", however, the numbers immediately below indicate that it will actually burn 70 percent of the fuel a Boeing 737 does - 30% less fuel.
(490/596)^2 * 145 MPG) = 98 MPG
737s are already on the slow end of airliners, but it seems like all the fuel savings in this design study come from just flying slower.