The issue here is probably that we don't explain how sample books work properly.
When you use sample: false, the chapter title still appears in the table of contents for the sample book. This is so people get an accurate understanding of how much content is in the "real" book, and the topics it covers.
But if you go to an excluded chapter in the sample book, you will see this:
Just to be clear, here is how it was done in this example:
{sample: false}
# Chapter Two
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.