Since we now know that some people can change their heart beat at will, their body temperature or their immune system response, and that it's something you can train, I don't think anybody find that very surprising. But good to know.
If I heard "control heartbeat", I'd think more like breathing, where one could "hold their heart" like they "hold their breath".
If meditation lowers heartbeat and temperature, I imagine that it's "control" in the strictest sense, but I'd use "influence" or some other term if I was personally describing it.
A muscle is instant and precise.
> one could "hold their heart"
… now that sounds creepy.