It was an example of what would happen if you did. Nowhere in that comment, does it make the assertion that you are writing any book right now.

Do you mean that your students that this is content from your students so they are plagiarising content not you?
If so are they aware that you monetise their content for yourself?

What are your students' usernames here, please?

There is a setting for how rewards are used when you write a post.