Initially, he assumed that the dog was a wandering stray that had unintentionally boarded the carriage. That’s why he attempted to dismiss it from his thoughts. However, their story was far from over.
When he got home, he didn’t expect to ever see the dog again. However, to his surprise, he found the same dog waiting for the subway at the station again. And that was just the beginning, as he kept running into the dog over the next several days during his commute.