Raiders damaging other player's bases

Had a player call in a raid.  His base is at the bottom of a cliff.  Some of the raiders spawned in at the top and started attacking another players base and did a good deal of damage.  Screenshot after we stopped event.  Calling players base is on the right at the bottom (with the turrets on it).  Other players bases is on the left in the foreground.  The other player was not on at the time.