It's also very telling that he says he was "nominally a Christian", and that his experience of heaven is exactly what a Christian would expect. A luscious paradise filled with happy dead people. His vision sounds like a lucid dream, where "everything is more real - less dense, yet at the same time more intense."
And then he mentions how the woman in heaven turned out to be the sister he'd never known. Well, okay. Maybe he really did visit heaven and his sister Betsy. Or maybe the woman in his vision just happened to look a little bit like her. But remember it was four months after his vision that he saw the photo of his sister, so perhaps he just remembers the woman as his sister because he wants it to be true.