Did I just fry this thing?

I purchased an iPhone 6 on Craigslist about a month ago. It was throwing an error 53 when attempting to restore in iTunes which is supposedly linked to the Touch ID. This is supposed to happen when the original button is replaced, but it could also be from the button connecting it to the motherboard becoming damaged. He got the phone from the original owner and it worked until he tried restoring it. He was told the screen was indeed replaced.

Backstory aside, I bought a new long flex cable just to see if it was that. Rather than reassemble the phone completely I plugged all the cables back in to test it. I must've plugged the touch ID into the flex backwards because the button became hot (probably shorted). I unplugged it and reversed it, but I'm not getting anything now - not when I hold the power button, nor the home button, nor both in combination, or when I plug it into the PC or when I pull the battery.

So did I just kill this poor thing? If so, let this be a cautionary tale and let other learn from my idiocy because you can plug in the Touch ID cable backwards effortlessly.