apt update shows available packages, but full-upgrade shows none upgraded

I just noticed this while updating:

hiigaran@hiigaran:~$   sudo apt update [sudo] password for hiigaran:  Hit:1 http://archive.canonical.com/ubuntu disco InRelease Hit:2 https://dl.winehq.org/wine-builds/ubuntu disco InRelease          Hit:3 http://ppa.launchpad.net/graphics-drivers/ppa/ubuntu disco InRelease                                               Get:4 http://security.ubuntu.com/ubuntu disco-security InRelease [97.5 kB]                                                                          Hit:5 http://ppa.launchpad.net/libreoffice/libreoffice-prereleases/ubuntu disco InRelease                               Hit:6 http://archive.ubuntu.com/ubuntu disco InRelease                                                                  Get:7 http://archive.ubuntu.com/ubuntu disco-updates InRelease [97.5 kB]                                    Hit:8 http://ppa.launchpad.net/teejee2008/ppa/ubuntu disco InRelease                 Get:9 http://archive.ubuntu.com/ubuntu disco-proposed InRelease [255 kB]              Hit:10 http://ppa.launchpad.net/mozillateam/firefox-next/ubuntu disco InRelease     Get:11 http://archive.ubuntu.com/ubuntu disco-backports InRelease [88.8 kB] Fetched 539 kB in 2s (262 kB/s)      Reading package lists... Done Building dependency tree        Reading state information... Done 1 package can be upgraded. Run 'apt list --upgradable' to see it. hiigaran@hiigaran:~$   apt list --upgradable Listing... Done linux-image-generic/disco-proposed amd64 [upgradable from:] N: There are 3 additional versions. Please use the '-a' switch to see them. hiigaran@hiigaran:~$   sudo apt full-upgrade  Reading package lists... Done Building dependency tree        Reading state information... Done Calculating upgrade... Done 0 to upgrade, 0 to newly install, 0 to remove and 0 not to upgrade. hiigaran@hiigaran:~$    

Running sudo apt update shows that there is a package available, which in this case is the package. However, upon running sudo apt full-upgrade, it shows no packages will be upgraded.

I’m not particularly fussed about getting this package. Just curious as to why this happened, as I’ve never experienced it before.