Relevant section of the introduction of the paper that the article is reporting on:

In an attempt to standardize allocation methodology, the European Commission’s Product Environmental Footprint Category Rules (PEFCR) (16) for leather was published in 2018. These rules use economic fractional allocation, a standard within LCA and PCF methodology, in which the environmental impacts are allocated by the ratio in price of multiple co-products, which in this case are edible animal products and cattle hides. Specifically, the PEFCR suggests allocating 88% of farm-level impacts to dairy, and 12% to the bovine carcass based on biophysical allocation. After slaughter, the guidelines suggest 3.5% of carcass impacts should be allocated to hides based on economic value, (16) implying that only 0.42% of cattle production economic value is reflected in hide sales and purchases.

Basically the industry has just been equating economic value to estimated carbon footprint allocation, which is a fucking absurd assumption because it assumes a perfectly rational economy that aligns all activity to environmental impact instead of profit or opportunity. Sounds like the paper takes a supply-chain based view of the carbon footprint of each product. Like you’d assume they already did. The paper is very politely and verbosely saying that the industry has been massively fudging the carbon footprint estimate of leather, but if you do analysis the right way you’ll see that it’s much worse.