This study doesn't make any practical sense. These pages weren't designed to convey the maximal amount of information in the least amount of space, they were designed to sell a product. It's impossible to claim if these designs have a negative impact due to content dispersion or not unless you are measuring them against the purpose they were designed for.

They explicitly studied ecommerce/product pages here. The relevant metrics are which page had a higher perceived product value? Which page had a higher conversion ratio? Which page resulted in a higher NPS? Which page created a more positive brand affinity?

You don't sell portable speakers using specs, you sell it with aspirational images of it being used on a beach. Of course expanding an accordion of product details then asking "On a scale from 1-7, How well do you feel you understood the offering communicated on the page?" results in a higher survey score. If you said the more dense page converted better, then I would be surprised.

It's like designing a study on the negative impact of hard F1 race car seats, adding a bunch of foam, testing which is more comfortable, then proclaiming one is better than the other because it was rated more comfortable, when the only metric they were designed for is lap time.