Question 6.2.1, 6.2.2 and 6.2.3 are wrong

The question 1 is

Which of the following cases would all be covered in a Semver range of ^2.1.2?

^2.1.2 means >= 2.1.2 < 3.0.0, so the correct answer is answer B. You can find more about semvar on the link provided in the course https://docs.npmjs.com/cli/v6/using-npm/semver/

The question 2 asks which of the commands will execute both scripts. The only command in the answers that will execute both scripts is npm run lint && npm test. Now you can argue that it won't execute the second command if the first doesn't succeed but that was not the question and also one can argue that you don't want test executed if the lint doesn't succeed

The question 3 is

If a package dependency has a development dependency, in what scenario, if any, will the development dependency be installed?

So, although you're right about npm install would install devDependencies (of the app) the question is about package dependencies, or dependencies of dependencies.
As the course says:

An important characteristic of development dependencies is that only top level development dependencies are installed. The development dependencies of sub-dependencies will not be installed.