Hot rocks can be a source of CO2 but not methane to my...

Hot rocks can be a source of CO2 but not methane to my knowledge.

My suspicion is that these wells are probably located near an aquifer or other permeable rock unit and any methane generated has escaped. As you said CO2 preferentially adsorbs to coal over methane.

Structural conditions would need to be just right for trapping escaped gases and making a conventional play and it's a bit shallow for conventional. But you never know.

As they put down more and more wells they should be able to model CO2 vs methane saturation and hopefully will come up with both an explanation and a target for high methane, low CO2. That first well is definitely promising anyway.