Skepticism is an attitude which people have where they doubt knowledge which are considered conventional and <em>question the claims </em>or principles upon which the conventional wisdom are based on.
With this in mind, there are different reasons why a person would be skeptical about something such as:
When a source is unreliable
When the information is not consistent with available data
When there is a claim which has no supporting evidence, etc
Please note that your question is incomplete because you did not include the name of the book, so i gave you a general overview which should be helpful.
