All these battles over IP where there's an enormous power imbalance strike me as problems of ego. In college, I made a website and I thought another student "stole" the idea. I considered my legal options, but I'm glad I stopped there, even if I did have a case. The other student was never a serious threat to my idea and in fact lost interest in the idea next year. So the only harm I suffered was to my ego that thoug…
In your example you probably did the right thing by not persuing. But you could have also persued and fought a needless battle. Or it could have gone the other way: You could have overcome yourself and even teamed up with that other person.
Finding people doing similar things can be very shocking, because it threatens your self image. But it is also a chance to learn and grow, because who other than the person doing similar things as you did is someone to learn from?