You are correct on both counts, and the offending plugin is:
Last set from /usr/share/nvim/runtime/ftplugin/c.vim line 22
But then, the question becomes: how do I override the settings forced by the plugin?
In traditional vim, doing:
autocmd FileType * set formatoptions=
in your init file overrides misbehaved plugins because the code is executed after the plugin loads.
neovim seems to do the opposite … which means you can’t override plugin behavior.
Is there a way to change settings After a plugin has loaded?