As I expected, they didn’t say who paid for the study.
There are HUGE INTERESTS at stake here, as the entire food industry is centered on carbs. Take those out, or even reduce them substantially, and you throw millions out of work, including thousands with high 6-figure and 7-figure incomes. They will ‘resist’, to use a bit of Snowflake terminology.
As to fiber itself, the low carb diets actually do recommend fiber, as you get that in nuts and related items (along with some, but varying amounts of carbs), which they consider very healthy.
It would also be interesting to see how they controlled for other factors, such as weight - my guess is that they ignored the much higher percentage of overweight people on high carb versus low carb, and instead just compared people in the same weight bands - if so, they’ve ignored a huge benefit of law-carb, which is the weight loss.
Thomas Sowell had a (stolen) phrase for studies like this. He calls it: “The Empire Strikes Back”. He was using it in an education format, but it probably is the case here, also.