Unable to make Android library resources private?

Question

created public.xml in values and added public resource there

<resources>
<public type="drawable" name="image_public"/>
<public type="string" name="external_module_string_res_public"/>
<public type="layout" name="activity_main_public"/>
</resources>

but still, I am able to access to all resource from library module in the Main project.

tried this Chris Banes's instruction and this as well stackoverflow post

using Android Studio 3.1.4 and classpath 'com.android.tools.build:gradle:3.1.4'