Forgot to turn off Hotspot, tethered via USB along with direct Ethernet, end result?
I actually think there's little reason to be concerned, provided in Settings > Network, your Wi-Fi or Ethernet is ahead of iPhone USB in the left-hand list. OS X will go down the list and pick the first network provider that it needs to. So long as your WiFi stays up, you're fine.

I confirmed this by opening Network Utility and examining the transfer stats. You can see in the attached screenshots that all the action (packets) are happening over WiFi, hardly anything over iPhone USB.