No. IMO their assessment is not accurate based on my 30 years experience as a professional photographer.
I say that in larger part because of the IIIa Color mode option available on the D50 that influences the colors in the final photo.
But don't take my word for it. Look at a more in-depth and unbiased review of the Nikon D50 and the D40x -
Nikon D50 Review: Digital Photography Review
Nikon D40X Review: Digital Photography Review
Both the D40 and D40x use color mode IIIa as their default color mode...so...that point doesn't make much sense. The D40 is two, to three years newer, depending on how one looks at things like this. The D50 is from 2005, the D40 from 2007 or so, but the sensor development pre-dates the introduction. Regardless...the D40x has better color, and slightly better dynamic range, but it is still relatively "old", and is also kind of low-end.
My preference would be the 10MP D40x for the higher MP count, newer sensor, and the ability to use PRE-Ai lenses, which the D50 and D70 series, and indeed almost all other Nikons, can NOT accept. Some of the pre-Ai Nikkors, like say the 55mm f/3.5 Micro-Nikkor macro lens, sell in the $35 range...because they are, well...pre-Ai, and there's not many cameras that can use them unmodified EXCEPT the baby Nikon d-slr models D60, D40,D40x, and the D3xxx an D5xxx series models, and the new Df model.
Neither is a slam-dunk one way or the other. Both are "older". I think you're making a mistake going back THAT far. D80's here are $145, body only.