Wll, it's a tree that is collapsed into an array - which makes it an array to all intents and purposes.

The point is that the "tree-ness" is never exposed to the user. This is the problem OP is claiming to have solved - the cognitive burden that the tree solution introduces.

The point is that the "tree" is not exposed to the user. I feel the author makes this extremely clear.

This is still an acyclic node graph, it's just implemented as a tree.

Yes a linked list is a degenerate tree, but was this worth pointing out?