All users data showing for different users after addition of external usb hdd

I successfully installed NC on a VM. I was able to successfully mount a remote external USB storage connected to pi NAS on the same network as my NC VM. my issue now is that all users are seeing each other files. what did I do wrong?
if user1 upload a photo from their mobile , user2 will see it in the nc client and web!

No idea, you didn’t provide enough information to go on. How, specifically, did you “mount” this “remote external USB” in your NC VM and/or within NC?

One way I can think of this happening is if you mounted it as an admin in the global External Storage and set it to be available to all users.