Arch Linux X11 Gnome display settings show extra, nonexistent monitor. Why?

Doing my first Arch Linux installation. Previously I’ve only used a bit of Fedora, so I’m pretty new. Upon install and getting things all set up, I’ve found a strange problem. The display settings seem to show the existence of an extra monitor that does not physically exist. I have an array of three 1080p monitors (pictured), but the settings show the existence of an extra 1024x768 monitor. What on earth is going on here?

P.S. - I just used FFmpeg to rescale that photo for upload instead of finding some crappy online tool to do it. Linux is cool.

system specs?