In order to be eligible to win in the promo, the post has to be a question or response in the forum of the promo that is not in the welcome thread. It does not have to be directly about the book. It does have to be on topic to the forum. All four of these individuals asked or replied to a post about JDBC.
The way we generate winners is via an automated program. It gives us a randomized list of posts. We then go through it in order excluding people who are not eligible (the book promo team and the author). If a moderator tells us they have the book or don't want it, we skip them as well. Campbell was one of the first four names drawn. He expressed that he'd rather someone else get it. So I went to the fifth candidate who was Rahul.