Board Thread:Theories and Speculation/@comment-34277398-20190309153341/@comment-32685487-20190315015651

Hiruzen was the one who paid for Naruto's apartment and for him to go to the Ninja Academy. He also bought Naruto clothes apparently. What doesn't make sense to me is that it seemed like either Naruto was too picky to eat the food at home, or Hiruzen did not buy him any food for his home hence he would be getting Ramen from the Ramen guy every day eventually. Hiruzen was used to Naruto's eating habits and the way he did things at his house, as Kakashi was the one who was surprised about the milk being expired when they went to Naruto's apartment while Hiruzen wasn't phased at all. I think Hiruzen just took care of Naruto from a distance, paid for everything and checked in once every blue moon. That was the closest thing he had to somebody in his life at the time so of course he would call him Grandpa etc.