If you copied the articles, yes. If you copied the design using none of their assets or code, no. Copying it definitely is, stealing it definitely isn't (at least not in the legal sense, the moral sense is debatable.)

You should have confidence that you will win because you can implement it better, understand the need better, can craft better solutions faster, and have better content on your network. If those things aren't true and all you had was an idea, unfortunately this was bound to happen.

Ideas alone are not defensible, practically or even legally. Successful implementations thereof can be however.