I'm sorry to hear about this, what type of person would do something like this? Why can't they get their own content?
NO! You are not over reacting at all and you are well within your rights to be pissed off. How is this any different than if someone snuck into your driveway in the middle of the night and stole your car? There are way too many people who are too lazy too do anything on their own. Instead they spend their time and efforts looking for ways to cheat and get something for nothing.
I had this the other week where someone copied my content. I told them that Google will ban their website so they removed the duplicate content.