Encrypted home partition accessible by administrator

[Colin Law]

I am experimenting with encrypting a users home partition. I created a
new user using
sudo apt install ecryptfs-utils
sudo adduser --encrypt-home username

which appeared to do the job, however I see that when logged in as an
administrator (not the new user) I am able to browse the encrypted
files in Nautilus by using the administrators password.  Is that
supposed to be what happens?  If so how can I make a user whose files
cannot be seen by any other user?

Colin