As reported in https://bugzilla.gnome.org/show_bug.cgi?id=745258
"You can open these two files with Evince
Evince displays both images very similarly and with a quite thick linewidth.
Okular displays them much better and you can notice the difference in linewidth.
Printing to paper works correctly in Evince."
Created attachment 126919 [details]
Comparison between the output of pdftoppm and pdftocairo
The image contains in the top the output of pdftoppm and in the botom the output of pdftocairo.
Using pdftoppm is clear the difference in the line width. With pdftocairo both drawings look similar.
Tested with poppler 0.47.0.
Created attachment 126920 [details]
PDF Test case with the files linked joined in one single document