Your heart reacts to messages recieved through the body so when you exert yourself it and your breathing pick up to compensate, this is subconcious but reacts to fear, pain and even cold conditions.
Rock music (or what he's refering to here I think is the back beat, sometimes even called the hesitation heartbeat ) has, of course been connected to altering (and this is the important part) the normal at rest heartbeat. The science never once suggested it was harmful nor that it was only rock music that caused this effect.
The study only confirmed what was pretty much known, that music effects us physically and we may even synchronize ourselves to it's beat or rythm. The overall study suggests music developed out of our natural bodily rythms and explains why the urge to enjoy and produce music is inant in all humans.
Teenages are much more likely to go from rest to adrenialin high activity then adults and therefor (in most cases) prefer the faster, harder music than adults, it suits their biological state more. As one grows older they generally listen to slowe, steadier music perhaps even as a calming effect.
As I go back in my tape library I find much that I grew out of liking from my teens to 40 or now 55. Zeppelin, Floyd and the Beatles are still holding up but the bands that stayed in one vein of cadence bore the Hell out of me now. Even the fast stuff, because you have to be interested in it also or you just filter it out.
It's why people my age are lifetime Beatles fans I think : Because of the scope and cadence and music styles they incorporated they were more varied and wider than any other band. Some of their songs we didn't care for as kids, and skipped over, we found we liked years later, sometimes better than their hits. It's why by Rubber Soul days people in their 50s and older who hated the earlier pop Beatles found themselves liking some Beatles songs as the stuck in the 60s rock or Merseybeat kids started hating some of their material.