A slight rewrite makes this a reasonable question in Java. A list of lists has a tree structure and asking candidates how to print the items in a tree in depth-first order is reasonable.

The main issue is that you'd never use a list as a tree node in Java. There would be an explicit Node class of some sort.

I do ask a question where one possible solution is to define your own Node class, build a tree, and print it out. But you can also solve it without even realizing you're working with a tree.