What makes you think that? The author is the one claiming the result, which is that people who study science (which is amoral, not immoral) tend to be good people, is counterintuitive. If anyone, the author is the one in confusion.

If you thought he could've meant that people who aren't good could be amoral instead of being indecent, then you are most likely, although not absolutely wrong. Keep in mind amorality for a human is not well-defined, it is more often used to describe non-intelligent life or abstract entities. Society would consider an amoral person "immoral" in a casual sense of the word, because a person who is indifferent towards morality is per definition likely to commit immoral acts if there are no repercussions.