It takes a very artistic eye like yours to spot a potential shot like this. Most folks wouldn't even have noticed, but you captured this very eloquently. You're right. The light shining on the stones looks like a UFO. Did you set this up, or was this just some weird overhead lighting on the street? Either way, it's an interesting perspective.
Think about the photo before and after, never during. The secret is to take your time. You mustn't go too fast. The subject must forget about you. Then, however, you must be very quick.
Henri Cartier-Bresson
Roger