This is not your fault, but there is currently a GPG key collision with your Ubuntu apt repo key, which results in an illegitimate key being installed alongside the legitimate key. I noticed this by installing your key using the command in the guide:
$ apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 0xFDA5DFFC
Executing: /tmp/tmp.J95LwFsR4U/gpg.1.sh --keyserver
keyserver.ubuntu.com
--recv-keys
0xFDA5DFFC
gpg: requesting key FDA5DFFC from hkp server keyserver.ubuntu.com
gpg: key FDA5DFFC: public key "Totally Legit Signing Key <mallory@example.org>" imported
gpg: key D9B78493: public key "NzbDrone <contact@nzbdrone.com>" imported
gpg: Total number processed: 2
gpg: imported: 2 (RSA: 2)
Note the “Totally Legit Signing Key” that is imported.
It seems someone is trying to make a point that the short key IDs are insecure, and this is fair enough. More information about this is here, in case you aren’t already aware: https://dev.gnupg.org/T4136