ER's manifesto wasn't originally printed in a book format.
Originally it was created as an electronic document that he either sent as an attachment or sent a url of it in an email.
Disclosure by Santa Barbara County sheriff's department corrected earlier assertion that deputies were unaware of any videos
www.theguardian.com
"One minute later, he emailed a lengthy written manifesto to his mother, father and therapist that also detailed his plans and contempt for everyone he felt was responsible for his sexual frustrations and overall miserable existence."
Even if years later it was printed in its entirety in book format for criminology students to use for study, the pg 118 in the original document likely wouldn't match up with page 118 in a printed book version--which would likely have acknowledgements, a forward, maybe even an introductory chapter and/or index before it even got to the manifesto. Differences in formatting between a typed electronic document and book copy would also cause the page numbers to be the same.
Patterson's book makes several stretches, if not leaps in assuming thing or creating assumptions in the readers, IMHO.
Sure, it's possible that by some coincidence on page 118 of one of BK's book there was something about ER....but I can guarantee the underlined passage could not and did not correspond to whatever was on page 118 of ER's original manifesto document.