These are called FFC connectors and you already encountered them in step 5. FFC connectors have a locking mechanism (known as a flip lock) and must be opened before removing the cable. It is unfortunate that yours broke -- the tiny flip locks can be somewhat fragile especially when not opened. If you still have access to the unit then it is worth knowing that such connectors can be repaired using glue like cyanoacrylate fairly reliably.

I don't agree that the unit is not made to be upgradeable because in all honesty it is a tinkerer's dream. Mine has ram upgrade, touch screen, keyboard upgrade, 9h battery upgrade, massive SSD and 4 operating systems installed!