Mood: The mood of this video appears to be romantic and nostalgic, with a hint of melancholy. The theme seems to revolve around love and relationships, given the title 'Kaise Hua' which translates to 'How did it happen' in English. The overall emotion conveyed is one of longing and reminiscence.

Environment: The setting of the video seems to be an outdoor location, possibly a city or town with brick buildings in the background. The couple is dressed casually, suggesting a relaxed and informal atmosphere. The presence of a bag slung over the man's shoulder implies that they may be on their way somewhere or have just arrived.