Miyamoto only made that statement because it's reflective of his highschool days when he had a crush on a girl and when people asked what they were, she said that they were "just friends" despite all his advances.
Even though he's been long married with a wife and has kids this still haunts him which is why he's so obsessed with keeping things kid friendly. He retreats to his childhood and made his entire life around it as a cope.
You cannot convince me otherwise.