There was also the fact that Zelda 2 had cheap enemy AI and was overly difficult. Other than that, it was an outstanding game. Also- it was hard to say what exactly to expect from a Zelda game, given that it was ONLY THE SECOND ONE!!!
At any rate, what they say is that it takes inspiration to Zelda II and the creators loved that game. I'm not sure it's accurate to call it a spiritual successor.