According to this article:
I just got off the phone with applecare support.
It IS an error, the Remote Disc icon is not supposed to be there. It is only meant to be installed on the macbook air. It seems like apple by mistake included it on the Mac mini install DVD's.
Confirmed by Apple (sort of):
If your Mac already has a built-in optical drive, or an external optical drive connected, you won't see the Remote Disc feature appear in the Finder or other apps.
Since the first article mentions it appeared in 10.5.6 (or earlier), it seems odd that something Apple has called a bug would still be in 10.13.1.
I know how to remove and re-create it, and it could be useful if my optical drive fails. But I know several other ways of using remote discs.
Is there any value to this if I do have a working optical drive?