Neovim comes with a number of different defaults than Vim. The defaults are meant to be more applicable to working with a text editor in the modern world. Compared to using Vim with an empty .vimrc, some of the more noticeable defaults include enabled syntax highlighting, sensible indentation settings, wildmenu, highlighted search results, and search-as-you-type.
You can check :help nvim-defaults from within Neovim to learn more about the defaults.
If you wanted to synchronize your settings between Vim and Neovim, you could add the following to your ~/.vimrc (which is hopefully symlinked to ~/.config/nvim/init.vim):
if !has('nvim') set nocompatible " not compatible with Vi filetype plugin indent on " mandatory for modern plugins ...