I'm no fan of this particular interview question, but the article takes it too far. You can figure out tortoise-and-hare algorithm by reasoning (I'm pretty sure I did the first time I've seen the problem - although not in an interview setting). The key is to recognize that there's a very limited number of things you can do given all the constraints: moving pointers is pretty much the only tool you have.

If it indeed took 12 years for the algorithm to appear, it's likely because finding loops in a linked list isn't a very common problem, not because the algorithm itself is that hard.