If I may weigh in on this pedantic question… I would suggest that it belongs under “Demo Board Tutorials”. Even though it uses the Go Puzzles platform, it is not really so much like a problem collection, but more like an interactive demo board, albeit with arbitrary navigation restricted for the sake of presentation. It could also be classified as a “Go Book” I think.
This actually reminds me of another publication, Spindrift: Leon Chen 4p's Original Tsumego, available now on OGS Puzzles!, which blurs the line between Go Book and Puzzle Collection.