Every game borrows concepts from each game before it just like all music has roots in older music and every patent is built on the patents of others before them.
If somebody seen a work you did wether its a game, music, painting, etc and copies a style from it you should be happy that your work made a good impression on somebody. If somebody takes your exact work and scratches off your name and put theirs there then I would get upset.
Some people get stuck in the past and never move forward like the highschool football player who only talks about his old games a decade after they moved on. Everything revolves around their 5 minutes of local fame instead of moving on with life. These people should be pittied for the empty shell of a life they now live and then ignored. This will eventually force them to move on after they cant keep talking about the same old thing anymore. There is nothing wrong with reminising with others about the highlights of your past, but if your life stopped after that point you need counseling.