Whose story is this old coat?

Hard to say for sure. It might belong to a protagonist dealing with recurring conflicts but in updated circumstances. Could be from a fictional world or even based on real-life experiences.

The novel Old Boy was from China.

Many important figures' stories are in the Old Testament, like Adam and Eve, Noah, and Moses.

The Old Man and the Sea was from America.

The coat might be a key element that drives the plot forward. For example, if the character with the coat is being chased because someone wants the coat, that would create action and conflict.

It could be the story of various characters. Maybe it's a fictional ensemble or focuses on a specific protagonist. Hard to tell without reading it.

It could be anyone's story that Rebecca Solnit chose to tell. Maybe it's based on real events or fictional characters she created.

It could be about a special coat related to Christmas. Maybe it's a coat that has a heartwarming story, like it was passed down in a family during the Christmas season, carrying with it memories and traditions.

Once upon a time, on a cold Christmas Eve, there was a little girl named Lily. She had an old, tattered coat. As she walked in the snow - covered street, she saw a poor old man shivering. Without hesitation, she took off her coat and gave it to him. The old man was so grateful. That night, Lily felt the true spirit of Christmas in her heart, even without her coat.

Well, it could be that he left his coat in your closet by accident. Maybe he was in a hurry and forgot to take it when he left.