"Cast Display" option showing up in my Quick Settings

I first noticed this today, and no my N5 is not updated to 4.4.3 yet. Stock 4.4.2. I've been using chromecast since it first shipped, but never messed with anything Miracast.

I don't have "Cast Displays", or whatever the miracast option is called, enabled in my display settings.

Pulled down my quick settings to check something, and saw this Cast option.

Tried to use it to send my display to chromecast, nothing.

What's going on here? Does my neighbor have a Miracast device that my phone is sensing?