This is a typo in the upgrade guide. It should state Sitecore 8.2 rev. 171121 (Update-6) Update Package.
In more recent versions of the upgrade process, Sitecore has changed the way they allow the update process to take place. If you take a look at the
.update package you will notice it is much larger than previously (Sitecore 8.2 rev. 171121.update is 466MB in size) and contains several update packages:
When you run the update installation wizard you are also present with the wizard step to select your current version of Sitecore:
The wizard should be clever enough to detect your current version of Sitecore and pick the correct version automatically (the above will only appear if it fails to detect it):
This "multi-step" upgrade path has been available for several (minor) releases now and allows a more direct upgrade, but make sure you have followed all the pre-install steps including upgrading the Sitecore Update Installation Wizard itself, a separate upgrade package is available and the above relies on this.
To answer your question directly, yes it is possible to directly upgrade from your current version but the upgrade documentation seems misleading. You should confirm this with Sitecore Support and ask them to correct the documentation accordingly.