You can know whether or not your mine got plundered in the event log, but these things are getting only players who got revenge on you, they choose from three options what to gift to the one who plundered you on which you got your revenge afterwards. Basically, this guy plundered someone in the mine, and that someone got revenge on him and gifted either the stamped breakthrough pill or the Chyo swimsuit poster/picture as saying - "hey, I got revenge on you, here's something from me to show you that how much I enjoyed giving revenge."

P.S. This is not mine reward, the topic title should require a changed because it is misleading. This is gifted item from revenge.