fish displays one "suggestion" as you type, which can be a file, option, or history item. You can use tab to get a menu, similar to the demo.

Showing everything as you type sounds neat, but in practice it's jarring to have your screen fill up the second you press a key. fish operates on the UI principle of progressive disclosure: be helpful but not overwhelming. That's why it only shows one.

fish knows how to parse man pages to extract options, so fish can tab-complete options even for commands that don't have explicit completions. It's surprising that nobody else seems to have tried this.