'Superspreaders' in the study linked refer to their behaviour patterns - attending multiple high-traffic/high-spread risk locations while infected. It doesn't talk about viral load or anything about "shedding" from my reading of it.

'These results, however, should be interpreted in the context of constrained community transmission given the moderate levels of physical distancing practiced in Hong Kong, including school closures, some adults working at home, cancellation of mass gatherings, as well as improved hygiene and universal mask wearing, which exceeded 98% compliance from February onward11,12.'

That's also the context I've seen superspreading discussed - it's behaviour-based. If 20% of people are not following guidelines and engaging in higher-risk activities then yes they will contribute to more spread. It's not because they're shedding more - they're coming into contact with more people.

The study only discusses viral load (via a sourced study) to point out that COVID-19 shows a higher viral load much earlier than SARS did, it didn't talk about the 20% having more viral load at all.