It's hard to say if that's even a choice for the lullaby. This person could have completely made that up for no reason at all. We're not on the set, the movie hasn't been released, and I don't think they've really confirmed what the lullaby sounds like or who write it.
I did hear somewhere (I think it was a Comic Con interview thing) that Robert made it up on the spot. That he started playing and they kept filming. I really hope that he wrote it (or made it up) because that would be unbelievably cool.
So unless this person somehow found the scene with the lullaby, and took the music from it (and if this happened I think they would post the whole scene) I don't think that's the real lullaby.