Comment # 1 on bug 997458 from Dominique Leuenberger

gpk-update-viewer does not do DISTRO upgrades - it only supports patching a
system.

With > 5000 packages this is unlikely to be a stable system receiving updates,
and as such the message is correct.

If you run Tumbleweed, the correct way to stay up-to-date is by using "zypper
dup" (each snapshot is to be treated as a new distro version)