It cites the ISS's centralized 16kW cooling system which is for a big space station that needs to collect and shunt heat over a relatively large area. The Suncatcher prototype is puny in comparison: just 4 TPUs and a total power budget of ballpark 2kW.
Suncatcher imagines a large cluster of small satellites separated by optical links, not little datacenter space stations in the sky. They would not be pulling heat from multiple systems tens of meters away like on the ISS, which bodes well for simpler passive cooling systems. And while the combined panel surface area of a large satellite cluster would be substantial, the footprint of any individual satellite, the more important metric, would likely be reasonable.
Personally I am more concerned with the climate impact of launches and the relatively short envisioned mission life of 5 years. If the whole point is better sustainability, you can't just look at the dollar cost of launches that don't internalize the environmental externalities of stuff like polluting the stratosphere.
It’s amusing that the article points out how large the radiators will have to be, when the proposals already include building giant radiators. Or that the satellites will have to be vastly larger than the ISS; surprise, surprise, that’s also part of the plan.