To be honest, though you were right to grill this person from a technical standpoint in the interview, I believe you crossed the line in your email back to this person.  To be honest, your tone and tactlessness was unprofessional in and of itself. 

Simply put, you could have simply said something more hr like. ...

While we reviewed your skills, we have selected a different candidate who was a better fit for the position.  Good luck in your job search.

That would have sufficed. . .