They’re probably basing their calculation on the orbital design discussed in citation 34: Suffern’s Some Thoughts on Dyson Spheres whose abstract says
According to Dyson (1960), Malthusian pressures may have led extra-terrestrial civilizations to utilize significant fractions of the energy output from their stars or the total amount of matter in their planetary systems in their search for living space. This would have been achieved by constructing from a large number of independently orbiting colonies, an artificial biosphere surrounding their star. Biospheres of this nature are known as Dyson spheres. If enough matter is available to construct an optically thick Dyson sphere the result of such astroengineering activity, as far as observations from the earth are concerned, would be a point source of infra-red radiation which peaks in the 10 micron range. If not enough matter is available to completely block the stars’ light the result would be anomalous infra-red emission accompanying the visible radiation (Dyson 1960).
Bolded for your convenience. Presumably they justify that assertion somewhere in the paper.
They’re probably basing their calculation on the orbital design discussed in citation 34: Suffern’s Some Thoughts on Dyson Spheres whose abstract says
Bolded for your convenience. Presumably they justify that assertion somewhere in the paper.