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
  syntax on                       " enable syntax highlighting
  set autoindent                  " copy indent from the previous line
  set autoread                    " reload from disk
  set backspace=indent,eol,start  " modern backspace behavior
  set belloff=all                 " disable the bell
  set cscopeverbose               " verbose cscope output
  set complete-=i                 " don't scan current on included
                                  " files for completion
  set display=lastline,msgsep     " display more message text
  set encoding=utf-8              " set default encoding
  set fillchars=vert:|,fold:      " separator characters
  set formatoptions=tcqj          " more intuitive autoformatting
  set fsync                       " call fsync() for robust file saving
  set history=10000               " longest possible command history
  set hlsearch                    " highlight search results
  set incsearch                   " move cursor as you type when searching
  set langnoremap                 " helps avoid mappings breaking
  set laststatus=2                " always display a status line
  set listchars=tab:> ,trail:-,nbsp:+  " chars for :list
  set nrformats=bin,hex           " <c-a> and <c-x> support
  set ruler                       " display current line # in a corner
  set sessionoptions-=options     " do not carry options across sessions
  set shortmess=F                 " less verbose file info
  set showcmd                     " show last command in the status line
  set sidescroll=1                " smoother sideways scrolling
  set smarttab                    " tab setting aware <Tab> key
  set tabpagemax=50               " maximum number of tabs open by -p flag
  set tags=./tags;,tags           " filenames to look for the tag command
  set ttimeoutlen=50              " ms to wait for next key in a sequence
  set ttyfast                     " indicates that our connection is fast
  set viminfo+=!                  " save global variables across sessions
  set wildmenu                    " enhanced command line completion
endif

I've left some short comments, attempting to briefly describe each one of these settings, and you can learn more about them by checking the corresponding :help entry.