But it does matter that you decided to publicly out him. This is very petty and as a user i would feel betrayed of my privacy.
You could have actually taken advantage of this and wrote a completely different blog post and people would have appreciated it, but this feels too petty. Even when you say it doesn't matter and all the diplomatic cliche saying competition is good, it just doesn't feel right because I can sense the bitterness in every word.
It's not like this guy was freelancing for you telling you he's going to build your idea and one day suddenly he launched it as his own. You already have a service out there. It's public domain. You can't "steal" an idea that's already out there.