They seem to be talking about bodybuilding a lot, but then (at least some) of the discussions move to muscle growth among random groups of people. The two are not the same. Bodybuilders are trying to put on muscle, sometimes in specific places, long after they have stalled in workouts most people would do. >Going on a higher carb diet increases intramuscular glycogen stores, which attracts a lot of water into the mus…
You don't eat carbs for the pump. It's right there in the paragraph -- you eat carbs to have glycogen, so you can lift more. Then you stop eating carbs to get shredded. Your own quote just says it is an effect, not that it's the purpose.
And he's saying the article is wrong. People love hate bro science but most bodybuilders go through a lot of trial and error to find the right diet. And they don't meassure success by looks* but by performance (eg. new PR). The article basically thinks that bodybuilders don't actually know what they are doing when most actually do. Maybe not all understand the exact science (although some certainly do) but they do know what works, because they exist as a community of millions of people all trying things are reporting what works.
*some do, but the ones that do are not eating carbs