Every assumption the author makes is derived from baseless speculation. Your projections are entirely inaccurate leading you to conclusions that are utterly bogus. It was an interesting supposition – but ultimately a false one. NFE (nearly free energy) would be a boon to the entire planet. NFE means a higher standard of living for every human being. Energy = Life.
(Caveat: there is no such thing as NFE!)
• As others have pointed out the fraction of additional heat would be miniscule compared to what the Sun rains down on us daily. And in fact, as the CO2 levels would begin to drop (no fossil fuel burning) the escaping radiative energy would increase.
• It’s a common fact that as standard of living increases population drops. So much so that eventually, with or without NFE, the entire world will be entering a low fertility phase. Under such circumstances you should be worrying about a reduced population not an exploded one.
• Huge swaths of non-arable land are begging for development. All they need is a little NFE to produce water and fertilizer and the reduced well-off population of Earth would be able to spread out. Just the opposite of your projection. The de-urbanization of cities may become a problem however.
• Traffic problems? Please! Why truck anything when you can 3D print or grow whatever you need in your backyard NFE fueled greenhouse? Self driving/flying personal cars, copters and dirigibles will soon be a reality. The only reason traffic exists at all is because humans are forced to live in dense cities. No need for those if NFE were to allow for the full colonization of the planet.
• Mineral resources? Yes, they would be a problem if all we had to work with was a single planet’s worth. But NFE would provide the ability to leverage off-planet resources. As futurists have already started planning, Moon and asteroid mining will be a reality in the coming centuries. No resource restrictions there.
So, sorry, none of your assumptions prove correct whatsoever. Better luck next time.