It says: "There are currently 2 active/semi-active branches" and then proceeds to list 3. The last of those 3 should be "13-CURRENT", not "12-CURRENT".
A commit references this bug: Author: emaste Date: Tue Nov 26 17:47:07 UTC 2019 New revision: 53641 URL: https://svnweb.freebsd.org/changeset/doc/53641 Log: FAQ: update branch count and names CURRENT is 13-CURRENT, and there are 3 active/semi-active branches. PR: 242204 Reported by: PauAmma Changes: head/en_US.ISO8859-1/books/faq/book.xml
Fixed.