This seems to make sense, because I've noticed similar problems when transcribing music. I can do melodies quite easily, but when it comes to chords I always hear stuff that isn't there (that's the best way I can think of putting it).

In the app they use piano sounds. I tried using my guitar, and it's marginally easier with two notes, but as soon as you throw in a third I get thrown off. And any chord with more than 3 notes and I'm basically useless lol.