I have to disagree--at least as far as my personal situation is concerned.
My childhood had its ups and downs, its slings and arrows, to be sure. For the most part, though, my formative years were happy ones.
I had a basically positive high school experience. I wasn't the homecoming king or the captain of the football team; but I liked most of my classmates, and remain in contact with many of them to this day. (I graduated from high school in the antediluvian year of 1986.)
So was the writer who was interviewed completely full of horse pucky?
Not exactly. I do believe that there is a connection between writing fiction and introversion. As a writer, you have to spend a lot of time in your own head. That may sound pretentious, but I really don't mean it that way; it's actually a practical job requirement.
I was recently paging through one of my old high school yearbooks, and I came across a photo of myself (one of those random "slice of high school life" shots that yearbook compilers tend to love). It was a golden early fall morning, during the homeroom period, and I was staring out the window of a second-floor classroom, onto a grassy courtyard below
I can't claim to remember the day that photo was taken; but I do still have memories of the classroom, the window, and the courtyard. I was a daydreamer, even then.
Not an unhappy daydreamer, mind you-- but a daydreamer, nonetheless.