Give that podcast a listen if you are interested. Speculation wasn't the right word to use. Behavioral and cognitive evolution is very real, but also very fuzzy.

The strong relationship between language and music in the human brain has been long established in neuroscience through a number of experiments.

What I found to be uniquely interesting about this theory is that where we already knew that our ability to understand music is deeply related to our ability to understand language there is now a theory that explains how this relationship evolved and why that relationship has to be so.

The dopamine response to song provides a clear evolutionary benefit. For birds that benefit seems to be limited to mating. Humans are a eusocial or prosocial species. Both the ability to positively regulate the mood of other members of a society and the ability to have your mood positively regulated by others is an extremely beneficial adaptation. Extreme isn't a strong enough word. These abilities are likely hard requirements for intelligent prosocial species. Selection pressure for cooperative and affinitive behavior would have been immense. Humans have developed prosocial abilities in many ways. Ability to enjoy music is an example of one of those abilities

Understanding music would then be something that just comes with the ability to learn vocalizations, speech and language. As we evolved speech and language abilities, the ability to understand music just came with it. Enjoying music as opposed to just comprehending it is an exceptionally beneficial adaptation for a member of a prosocial species.