It's in the article :
"Samsung’s Auto Blocker feature takes things a bit further.The feature, fully blocks the installation of apps from unauthorized sources, even if those sources were granted the REQUEST_INSTALL_PACKAGES permission."
I really don't mind that they hide the button to enable installs from .APK when they are being directly downloaded. It has been in my opinion very bad idea from the beginning that it shows that, it has enabled multiple malwares in android. Non-technical people should not have easy way to install things, even with big warnings, because people ignore warnings.
If google removes the ability to install non-store apps all together, then that day I will stop using Android.