Hmm, I would say even older than that (which, of course, is in no way intended to be a value statement of any kind, I like the website and the project, cool idea! :D).
If you squint a little, the linked project is basically a https://en.wikipedia.org/wiki/A*_search_algorithm with optimized implementation, heuristics and so on. I also think that A* was associated with AI due to its use in path finding in early robotics - But I am not sure!
On further reflection I actually now disagree that a an algorithm based puzzle solver was ever referred to as AI, even in the context of video games, in which AI refers to the behavior of NPCs.
Seems to be AI in the older sense from 10 years ago?