If you found this thumbing through the pages and it was not brought up on class, that itself could be more of a reflection on the attitude of the school toward guns. I seriously doubt that the information on firearms was a part of the schools choice to use that particular book. If they didn't bring it up in the curriculum than the school probably has no opinion on the matter or at least is not trying to teach the topic with a bias. There are many more important factors to consider than the slant on firearms when choosing a textbook on health to teach with.
On a similar note, the topic of gun ownership came up recently in my high school criminal justice class and after giving us some stats on murders with firearms the teacher showed us videos (news clips) for and against gun ownership. The pro-gun argument video covered concealed carry and had some big names I recognized and was very comprehensive and convincing. The anti-gun video (that one where they gave college kids fake guns and then had the instructor come and shoot up the classroom, NBC w/ Dianne Sawyer maybe, I forget) was there as a counter argument but the slant the teacher put on it was very pro gun. (in NY of all places) At the end the teacher asked for a show of hands for opinions and pro-gun won by a landslide.