Command line/shell -unclear learning objective (built-in commands)

[juliebates]

Example of unresolvable build in commands 'which' and 'pwd'

I wasn't sure what I was supposed to learn from the illustration

a) what is relationship between 'which' and 'pwd' as not built-in commands, or IS that the relationship between them, that both are NOT built in, and therefore both yield 'invalid option' results?
b) mention of which as built-in command in zsh suggests possibility of including that in the illustration-- paired example of built in versus not built in?