Why does typing 'q' exit vim? (.man file)

The Vim editor will load the man filetype plugin (ft-man-plugin) whenever it opens a file which has a .man filename suffix.

A more usable way of using this plugin is by loading it with

:runtime ftplugin/man.vim 

... and then using the :Man command, e.g.,

:Man ls 

One of the things the man filetype plugin changes is that it maps q to :quit. It does this because the :Man command usually runs within Vim, and quitting it brings you back to whatever other document you were writing at the time, and someone decided it would be handier to just have to type q, as you would usually do to exit out of the manual pager in the terminal.

For more information, see :help ft-man-plugin in Vim.

To avoid loading this plugin for .man files, set the filetype of files with this filename suffix to something else, e.g., text, in your Vim startup file (~/.vimrc or wherever you configure Vim):

autocmd BufRead,BufNewFile *.man set filetype=text 

Or, remove the filetype detection completely for these files:

autocmd! filetypedetect BufRead,BufNewFile *.man