Sorry, didn't see your comment until now! :)
I think you didn't get hit, but rather got the notes right (per chance?) just before you got hit. The whistling detection acts quite randomly, depending on your mic and surroundings... We tested it on 5 devices in different rooms and unfortunately never got it to work reliably in all those situations. As we barely got all the systems to work in time, the game definitely lacks in optimization, feedback and polish. ;)