Files saved to external SSD show as also taking space on internal storage ???

So I have the base M4 Mac Mini and have just setup an external nvme with my home folder on it. (Also created a backup user account in case any issues arise of course) My problem is whenever I copy files to the external drive, when I go to system settings it shows as taking space from the internal drive as well as the external one ! If I delete the said files off the external drive then the storage increases on both nvmes... Am I missing something ? The whole point of using an external drive was to offload all the apps and files to an external drives so why is it now showing as taking the storage space in both ? Is it a known bug ?