If so, that could make for either a very unfortunate surprise (i.e. a spacecraft passing through that point suddenly melting to a crisp) or an interesting source of energy if it could be harnessed.
The argument about reversibility is kind of a straw man: it answers "why can't you concentrate all light on a single point" while the real question would be "why can't you concentrate light on a smaller surface" (which you can do actually).
Similarly for the conservation of étendue: maybe you can't "swoosh the light rays closer together" but that also doesn't say you can't concentrate beams on a small surface, which might be sufficient to start a fire.
So really it all comes down to the thermodynamic argument, which has its own problem: it only works if you assume that moonlight has the same temperature as the moon. There's nothing in the article that mentions or justifies this assumption. And obviously a mirror can reflect light that is much warmer than itself, so you definitely have to explain why that's not the case with the Moon (e.g. its albedo and heat dissipation are too low).
(However I love the drawing of the encircling sun, it's great to make the point that no matter how much light you concentrate, it won't heat the body warmer than the light's temperature).
With a mirror you can also burn things if you focus sunlight, but the surface of the mirror stays cool.
An atmospheric lens, however, will reach a maximum of somewhat closer to solar surface temperature, though still lower because of scattering and absorption which definitely isn't trivial on this kind of scale.
https://www.universetoday.com/19981/moon-albedo/
If it had an albedo of 0% it would be a black body and be radiating only thermal radiation at its surface temperature; it's not too far away from that but it is reflecting some "black body" radiation from the sun representative of a higher temperature.