Who is The Young Construction Worker from The Madonnas of Leningrad: A Novel and what is their importance?

In the novel's final moments, the elderly Marina, now deep into the late stages of Alzheimer's, is portrayed as having again wandered away. She is discovered by a young male construction worker who describes her as happy, speaking a foreign language, and behaving as though she's guiding a tour, a tour that he says is showing him the world. It is through this young man's experience that the reader comes to understand not only that Marina has withdrawn completely into her past, but that she is happy and safe there.