The Wavefront Errors mentioned in the article assumed Peak-to-Valley Wavefront Errors at 550 nanometers.  A group of renegade optical companies are challenging the Peak-to-Valley measurement in favour of an RMS Wavefront Error they claim is more representative of a mirror's actual performance.  This measure is more forgiving than the Peak-to-Valley measurement in that it burys the highest peak and lowest valley in a statistical average.  It also brings some confusion to the marketplace because its statistical fraction of a longer wavelength of light produces a common fraction that as a Peak-to-Valley fraction would be far more impressive.  The RMS Wavefront Error: 1 / 14 of 633 nanometers, has the same magnitude as a P-V Wavefront Error that is 1 / 4 of 550 nanometers.  l/14 seems much smaller than l/4, but it's not. Saying that it is smaller, is like saying 1 inch is smaller than 25.4 millimeters because 1 is a smaller number than the number 25.4.
Caveat Emptor
For an optical instrument to meet the definition of a true telescope, the total instrument must be Diffraction Limited.  Since Wavefront Errors are cumulative, having one of the optical compontents (Main Mirror or the Secondary Mirror) meet the requirement is not good enough, because the other optical component would have to be absolutely perfect, which is simply not possible.  The minimal P-V Wavefront Error for each component is l/8 @550 nm. since 1/8 + 1/8 = 2/8 = 1/4. This works out to a minimal RMS Wavefront Error of l/28 @ 633 nm. as
1/28 + 1/28 = 2/28 = 1/14.