So a colleague pointed me to a resource that helps explain the problem.
https://web.archive.org/web/20201014190758/https://lists.freeswitch.org/pipermail/freeswitch-users/2013-October/100619.html (kudos to @ vikasgarg86 for finding and sending me that link ).
It turns out that it is this native
com.apple.ftp-proxy.plist live on
/System/Library/LaunchDaemons/com.apple.ftp-proxy.plist as guys
/usr/libexec/ftp-proxy (https://github.com/drduh/macOS-Security-and-Privacy-Guide/blob/master/launchd/15B42_launchd.csv#L94) which apparently binds to TCP port 8021.
Disabled Label com.apple.ftp-proxy UserName _ftp Program /usr/libexec/ftp-proxy ProgramArguments ftp-proxy -p -n -V -D3 -t1800 inetdCompatibility Wait Sockets Listeners SockNodeName localhost SockServiceName 8021 SockType stream
However, it is only halfway in understanding what is happening. What the original author of the call that was connected here could not find out and myself, is how the service got there in the first place. Why does it even work? and what are the consequences of changing the port from 8021 to something else.
Please comment below if you know the answers.
By the way
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.ftp-proxy.plist does the job of stopping the service.