[KacypeJeope]

Assuming it's not metaphorical, I presume he means that the blast caused human-shaped patterns to be made on the pavement because the blast hit the human, and therefore hit the pavement/etc. behind them less significantly in the area their body shielded than the area around their body.

My bet would be metaphorical though (the shadows of the people = their memories, things to indicate they were there, etc.)