SourcesList in Debian Wiki wrong?

I had the following in my sources.list file:

deb http://ftp.uk.debian.org/debian-security buster/updates main contrib non-free

Based on the example sources.list entry at the Debian Wiki:

deb http://deb.debian.org/debian-security/ buster/updates main contrib non-free

But this got me the following warning:

E: The repository 'http://ftp.uk.debian.org/debian-security buster/updates Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default. 
N: See apt-secure(8) manpage for repository creation and user configuration details

I changed the line to the following after reading a post at Stack Exchange (changing stretch for buster):

deb http://security.debian.org/ buster/updates main contrib non-free

Which worked -  Thanks Stephen Kitt.

Stephen's source link however goes to the security information page at debian.org which has the following example:

deb http://security.debian.org/debian-security buster/updates main contrib non-free

I admit to being a bit confused. But I am also tired and my brain isn't working - it's end of term and I have young children.

So I am just going to post this and hope that either somebody will clear up the mystery or I can come back to it later when my brain is working and clear it up.