facetime showing a number I didn't call
Sometimes when wanting to chat with someone I accidentally press the FaceTime option instead of a traditional phone call. Perhaps you might have done so at some point? Or maybe it will log if another person attempted to call you (accidentally) and then hung up?

The other possibility is iCloud syncing Call history. Since iMessage and FaceTime don’t affect the carrier - Apple could sync that history if iCloud is signed in on two devices. 

Lastly, handoff could also be in play. Again - look at the iCloud accounts on all devices such as Mac and iPad and iPhone.