Your panels might be 3x more productive, being in sunny Australia. Where does the author live in the US? I either missed it or he didn't say. Even then, the layout of his roof could have a big effect.
Another point is that certain solar panel imports are tariffed as much as 30% in the US in order to protect the (non-existent?) domestic solar panel manufacturering industry. But it appears Biden temporarily suspended it about 6 months ago. Unclear whether this added to his purchase price.
Author mentions New England, which I gather is a large-ish area, but let's say about 44 degrees north.
I'm 33 degrees south, so obviously 'better' in terms of solar potential. We probably also have fewer cloudy days (though much hotter days during summer, I'm not sure how that compares out over the year).
My panels are not optimally installed, at least not optimally for capture - but definitely optimally for installation cost. I have a gable-roof shed facing roughly NW, with 22 panels on the NW side, and 11 on the SE side. Roof slope is about 9 degrees.
I just start to flat-line my 10kW inverter, fed from 12kW panels, about 3 weeks (on the winter side) of the equinoxes - so there's definitely room to improve the configuration there. FYI in summer I generate average ~70kWh a day, and in winter about 30.
It sounds like author put these panels on in late 2021 --which should post-date the worst of the COVID-induced shipping/trade bumps, and pre-date the Ukraine / Russia induced effects.
EDIT: You mentioned "... tariffed as much as 30% in the US ..." -- I agree that kind of figure could be explained by duties, tariffs, etc, but the difference here is actually 3x (26k vs 9k) for a system that's only about 60% the capacity of mine. A like-for-like system, extrapolating from TFA's numbers, would be US$35k, or nearly 4x difference.
Another point is that certain solar panel imports are tariffed as much as 30% in the US in order to protect the (non-existent?) domestic solar panel manufacturering industry. But it appears Biden temporarily suspended it about 6 months ago. Unclear whether this added to his purchase price.