I have updated the description to put "(and still be a singly-linked list)" after each place that I said "share as many nodes as possible".

There are already two parts of the description that show that the list should be flat (in addition to just calling it a "singly-linked list"): there is a diagram showing list3 and JSON showing list3. I suppose that it would be more obvious if I had done the diagrams with a list constructed like your caba list, but what you created is not a singly-linked list, just something that obeys the same interface (mostly).