In section 2.3.1 "Prepare the Installation Media" the various types of installation files are listed off and briefly described, but not mini-memstick.img It is intuitive that mini-memstick.img is just like memstick.img with less stuff, but it is unclear what isn't included in the mini version that is in the main version.
A commit references this bug: Author: wblock Date: Fri Oct 21 20:31:12 UTC 2016 New revision: 49539 URL: https://svnweb.freebsd.org/changeset/doc/49539 Log: Explain the difference between memstick.img and mini-memstick.img. Patch provided by Tim Moore <timmoore88_gmail.com>. PR: 213468 Submitted by: Michael Necio <michael@necio.ca> Differential Revision: https://reviews.freebsd.org/D8252 Changes: head/en_US.ISO8859-1/books/handbook/bsdinstall/chapter.xml
Thank you!