What do you do if you have a nested data structure (like a tree) and want to print it in order? You write a simple BFS on it.
It's not even a question where you need prior knowledge on the algorithm, it's just logical. He could've easily asked "Print the contents of this tree to screen" and it would've been the same.
I can see how some questions like implementing quick or merge sort can be annoying, most libraries have a sort() function that usually implement either (or similar), you don't often have to write them yourself, but a BFS does not fall into that category in my opinion.
