As I recall, Solitaire is based on several seasons, not one, though the book only chronicles a year. If the book is art, and I'd argue that it is, then it only needs to be true to greater truths, not the day to day truth of the author's life. Obviously, he spent a good deal of time over several seasons alone. Just as it doesn' t matter that Thoreau went into town.
All poets do.
Products of the imagination. And thank god for that. I imagine that's why we find it capable of catching so much. Anyone can dictate the mundane moments of their day to day life. Artists shape the raw material of their lives into something more.