This industry can definitely be quite scummy. Even more sad, is when another indie studio does the same thing.
I actually had a sort of similar thing happen to me with my indie game, Ninja Exorcist.
https://ninjaexorcist.wordpress.com/
Before Klei entertainment even announced Shank 2, I applied for a job there, and showed them screenshots and designs for my WIP indie game, Ninja Exorcist, which was a side-scrolling, stealth-action Ninja game. At the time, there were very few stealth side-scrollers.
Then, fast forward numerous months later, after Klie announced, and then released Shank 2, they eventually announce Mark of the Ninja, an action-stealth, side scrolling Ninja Game.
Like, in all fairness, the general idea isn't exactly the peak of creativity, but I had never seem a game quite like it. It was super depressing to eventually find out how close the base concept for the game was to my own. It wasn't even a question that they ripped off the idea. In fact, they were close enough, and we had so many development speed bumps (we were a small team, two guys, who outsourced art), and the scope so big, we
weren't able to show the game or announce it until after Klei announced, Mark of the Ninja. We even had some guys try to shame us for ripping them off...
We also had an incredibly hard time getting any publicity for it. I often wonder if that was due to people believing we were ripping Klei off. In truth, the experience ended up deeply affecting my life on a personal level. It's just depressing that Klie didn't even have enough integrity to choose a different theme (why choose Ninjas? there are a million other ideas they could have done). It almost feels like they did it purposefully out of spite, or to run us out of business.