It is pretty clear from the article being criticised that the weight gains quoted are their estimate of the savings in their estimate of the skin weight based on their understanding of the static design loads on a typical central section of an A320 fuselage.
It is pointless to talk of percentage gains in fuselage weight when the baseline used is just a fraction of the total fuselage structural weight. Typically, fuselage structural weights lie in the range 21 to 23% of the aircraft empty weight. For an A320, that is a lot more than the 2155 kg quoted, so to talk of a 25% reduction in fuselage weight is a nonsense.
More to the point is that almost none of a typical transport fuselage is designed by the static loads. Depending on what part of the fuselage you are discussing, manufacturing (minimum gauge) limits, fatigue, damage tolerance and crashworthiness considerations dominate. Any actual weight gain will be the difference between the windowed design and the windowless weight that meets these more severe criteria, not the theoretical weight that satisfies the static load condition.
Nobody is disputing that removing the windows would save weight, although I am with tdracer in doubting whether it would be anything like the number claimed, neither would one suggest there was any real technical risk, but the commercial risks would be very large.
I'm not holding my breath waiting for an announcement that the next design to surface will be windowless!