I believe it is just an artifact of SMB shares as viewed on Macs resulting in a duplicate view of the same drive.
You don’t really have two drives - or even two partitions on the same drive. Further, if you navigate around the two apparent drives, then you will find that they have identical content. And if you add a file to one, you will see that it has appeared in the other.
Further, the NUC itself only sees one drive with one partition so it will not affect the operation of Roon.