Is that person using Mac Finder on their Mac to access the My Cloud if connected to the same local network as the My Cloud?
For remote access one would have to use the WD My Cloud Desktop program on their Mac or the MyCloud web portal to upload/download files. Or if using a v4.x My Cloud, install the CloudDAVMod to their v4.x My Cloud and map the My Cloud remotely or use the web interface to upload/download files remotely.
https://community.wd.com/t/app-clouddavmod-v1-0-for-firmware-v4-05-2016/161543
