Worth noting that one of the 5 listed NeoVim Non-Goals is "Turn Vim into an IDE"
He suggests neovim (and vim, emacs etc) fall into a category between text editor and IDE.
The term he uses is PDE (personalised development environment). In short, you have lots of power to customise your setup; you can give it some IDE-like behaviour but the way you do it tends to be by making personal choices of plugins and config.
It's not just a text editor, it's definitely not 'integrated'. I'm inclined to agree with him.
So the idea is Neovim by itself isn't an IDE. But it does enable you to build an IDE using configuration and plugins, or even embedding it in a GUI.