It's not an impostor the icon.library AROS 68k, probably it will be used for something, maybe to replace the one in RAM in case of deletion. or they forgot to delete it from the system, in fact on OS 3.1 exists only in ROM and in the OS it's not there

To install the icon.library of PeterK, first of all you have to download the most recent, this is because after a report of mine has been changed the path of ENV.... AROS uses a different path and without this change was not recognized def_icon, then maybe I'll attach the link where we have discussed with Peter.
Installation Icon.library PeterK
- Download
THIS Archive
- From the folder "Bonus" take the file "icon.library_Aros" and rename to icon.library
- Copy icon.library by Peter in LIBS and delete the one of AROS
- From the ThirdParty/RemLib folder take the file "RemLib" and copy it in C
- In the Startup- sequence add this command "C:Remlib >Nil: icon.library".
- You can put the command "C:Remlib >Nil: icon.library" after SetClock LOAD
If you have the dummy icons "the transparent ones created by the system" to make them active add the command "C:IconGhostingOff"
IconGhostingOff and other important commands for icons and more are in the same package of iconLib by PeterK