Yeah, some VPS do configure backports. It’s not a huge deal but in the yunohost project we kinda became a bit scared histortically about backports upgrading a shitload of stuff to incompatible versions.
You should run grep -nr backport /etc/apt/sources.list* to identify which line is problematic (in SSH from root or with sudo)
Then edit the file with for example nano <the file> and comment the line by adding a # in the front