No relation (I'm a co-founder). I'm guessing it's a case of convergent evolution. Our testing UI has been pretty similar since the beginning, 4 years ago (not sure if they existed then or not).
Edit: I realized after typing that it was confusing... I meant self-similar not similar to duolingo.
Is it me or the UI of their testing product looks very much like Duolingo?
Are they related?