The electromagnetic fields that comprise a photon are in a state of constant change. This change drives the central point of a photon forward through space. We measure the photon's path to be that of the central point, but the fields exist spatially around the photon at an amplitude that is greatest close to the point and diminishes as the square of distance away from the point.
When this photon nears its target, churning electrons belonging to atoms in the target begin to sense the photon's approach. Some electromagnetic fields in the electrons will be in good phase relation with the approaching photon. Among this huge jumble of moving electrons, some will be more inclined to absorb the photon's fields than others. Those most inclined will probably not be dead centre in the photon's path.