[sandgiant]

Good question! As most results in extra galactic astrophysics this one also depends on the cosmological model used. The actual paper linked in the article describes it well:

"The cosmic optical background (COB) is the average flux of visible light photons averaged over the volume of the observable Universe. It reflects, at least in part, an integral over the cosmological history of star formation occurring in recognizable galaxies, proto-galaxies, and star clusters (Conselice et al. 2016), as well as mass accretion by black holes (BHs) associated with the systems." - https://arxiv.org/abs/2011.03052v2

A common problem in astronomy is the lack of ways to measure things (we can't travel to the stars, yet). The special thing about this result is that it is a very direct and independent measurement of the background optical light in the Universe. This means it can be used to put independent constraints on the star formation history, as well as black hole accretion, and perhaps things we haven't even thought about yet.

Edit: And all those results are model dependent as everything else.

[_0w8t]

The article indirectly pointed out that the reason for previous overestimate was model error about solar system light background.

The biggest source of uncertainty with the new estimate is modeling of background light of our galaxy. Too bad that we cannot yet send a probe outside it to measure things directly.