Does landfill paper constitute a net source of GHGs or not?

Question

I thought it's scientific consensus that landfill paper, as any organic matter with low levels of lignin, is a net source of GHGs. But this Canadian paper of 2008 contains this unusual train of thought I have hard time following. Does it make sense?

Within the 90 kg of methane, 67.4 kg of carbon are ‘sequestered’, albeit it in a more greenhouse contributing form. An equivalent of 67% of this amount of carbon (44.9 kg) is emitted as CO2 from the remaining carbon through normal decomposition (Mikales and Skog 1996). The remaining 652 kg of carbon (2457 kg of CO2e) are effectively sequestered, due to the anaerobic conditions inside landfills. The net result is that paper in a landfill actually constitutes a carbon sink, sequestering 567 kg of CO2e per tonne.

From "The Environmental Impact of Paper Waste Recycling: A Comparative Study".

Answer 1

Landfill is a carbon sink only given either of the following two conditions:

1. You consider waste-to-energy "carbon neutral" (which would be totally ridiculous)
2. You store plant-based materials like organic waste, or wood, or paper, or cardboard, in the landfill, and make sure that they don't ever emit methane due to anaerobically decomposing or ever emit all their carbon as carbon dioxide due to aerobically decomposing

As (1) is totally ridiculous, the only reasonable way to consider landfill a carbon sink is (2).