I find it hard to believe - as far as I know this viewpoint is not mainstream. Maybe cherry picked, but more likely the study isn't a very representative or large enough sample. It could also be that these policies in theory should help the labor side, but in practice there are some confounding variables - ex. "well we would pay you more except for this pesky law preventing us, sorry" being used as an excuse, or general disdain for the idea of raising everyone's wages vs. stagnating most employees' wages save a few favorite employees / new hires.

Could also be that a requirement to post salary ranges gives companies better information on what the lowest wage is that prospective employees would truly accept.

I also find it suspect that the article is lumping together a study that focused on pay transparency and university professors, with a different study on a pay disparity law and saying their results suggest similar conclusions. They are different policies, different samples, and different effects - tricky comparison to make.

Was having trouble finding other studies, but here's a good place to dig around: https://scholar.google.com/scholar?hl=en&as_sdt=0%2C38&q=effects+of+pay+transparency+on+wages&btnG=