Are you talking about the ones at the bottom of the article? Because none of them said that the gap has got narrower. Paul Grayson and Eddie Jones both said that tier 2 nations have improved, but not that they are closer to challenging tier 1 nations.
I suppose you could argue that, in context, they were saying the gap was narrowing but neither are involved in coaching tier 2 nations at the moment and despite Eddie's comments, Tonga and USA lost all of their matches against tier 1 nations, including against Argentina which is one of the weakest tier 1 nations.
I think it is difficult to argue that the gap has narrowed, looking at the victory rate of tier 2 nations over tier 1 nations over the history of the world cup. Has the gap widened - well the results in terms of likelihood of victory suggest so, taking the most recent few world cups and comparing with the first few.
The article makes a point about reduction in average size of defeat (somewhat clutching at straws), but doesn't go all the way back. I think there is likely a trend here, but not sure it is related to the gap narrowing. I think it may be due to changes in the rules of the tournament.
First the introduction of bonus points has made points difference almost irrelevant, so once you are assured of victory and have scored four tries there is limited value in stacking up more and more points (particularly at the risk of injury), so I suspect teams take their foot off the pedal more than they might have done once.
Secondly (and probably more importantly) the number of replacements allowed has changed dramatically. So back in the days of 100+ points the weaker side would be playing the final quarter with largely the same team as started, with the stronger and fitter team running riot - now half the team can be fresh.
