...human cultures have sliced the pitch dimension into twelve distinct tones.

The researchers don't appear to have taken any note of the existance of those musical cultures that go in for half-tones and quarter tones. But then they also seem to have ignored the fact that most people don't speak English. Any research which exclusively concentrates on those would need to be extremely cautious indrawing any general conclusions.

I tend to assume that singing of one sort or another came before speech anyway. The same way it does with children.