update-alternatives
Reading the systemPackage: dpkg
Chooses which of several installed programs answers a generic name — which editor, which java. It is not a version manager: all it does is move a symbolic link.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
update-alternatives --display- Shows which implementation is selected for a given command, and what else is available.
update-alternatives --display iptablesis Ubuntu's documented check for this question.