I was pretty close in guessing what they believe was "wrong" (or really, superfluous) with their initial shell script example.

I'd even drop the "if" from their footnote version, and go with simply

  npm install || (echo "boom" && exit)

(Not exactly equivalent because there won't be an "exit" if echo fails, but it's my preferred instict over ";") Also, "(" starts a subshell, if we are being pedantic.