sh
ShellPackage: dash
On Debian and Ubuntu, /bin/sh is dash, not bash. A script that starts with #!/bin/sh and uses [[, arrays or source fails — in production, not in the terminal you tested it in.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
sh -s- Reads the script from standard input, which is what
curl … | shneeds. Anything after--is passed to the script.