The article also alludes to this, but doesn’t make it specific:
It doesn’t necessarily say much if a paper cites a paper that has since been retracted.
> Unlike (retracted, 2015) we found …
Or
> While (retracted, 2021) focused on … the present study concerns …
You’d need to do much more in depth analysis to determine to what purpose a retracted study was cited before you can establish whether there is a problem or not.