It's implied by his equating "feature" to "structure" and his references to a "Cosmological Principle" that "indicate that the structure of the cosmos is unifor

It's implied by his equating "feature" to "structure" and his references to a "Cosmological Principle" that "indicate that the structure of the cosmos is uniform on the largest scales" and that "this new discovery challenge the principle, which sets a theoretical limit of 1.2 billion light years for the largest structures." Think of it in terms of the Second Law of thermodynamics. Local increases in order (decreases in entropy), such as there formation of stars or the emergence and spread of life, apparently violate the law, but in fact do not when you look at a greater scope. Order is decreases at "the largest scales". So by "feature" and "structure" he means a local violation of this principle of uniformity. Apparently this arrangement of GRB's cannot be random non-uniformity, thus implying it is some kind of structure. For example if you flip a coin a million times you will get some clumsiness, periods with far more heads or far more tails. But if clumpy periods exceed a certain size, you would start to suspect that the coin is biased or rigged. It would be violating your expectations given truly random coin tosses. Or as skwosh said in another comment, "It's considered a feature I think not just because it's a ring but because it's an area of higher than expected density of Gamma Ray Bursts (GRBs)."