When you execute slackpkg update
command, slackpkg first checks whether your package list (not actual packages) is up-to-date or not. If package list is not up-to-date, slackpkg downloads new updated package list from the mirror you have chosen. When you execute slackpkg upgrade-all
command, slackpkg compares your list of installed packages with mirror package list and upgrades packages that have updated version in mirror package list.
No packages match the pattern for upgrade
Above message appears if your installed packages are all updated. Here "pattern" may refer to list of packages in the mirror, but I am not sure.