If you read the article it explains that bats and humans both have a structure called "false vocal folds" which can be used to make sounds as an alternative to the true vocal cords. These false vocal cords are what humans use to produce the growls in heavy metal (this has been known for a long time), and what bats use to vocalise (this has just been discovered).

Regarding your second point, if you think all research needs to be "for" something, then I can't help you.

I imagine they have similar vocal folds and equipment and the way metal vocalists use their equipment is similar. They don't have to have literally matching hardware to have similar features. Just like many animals have fingers and toes and we can compare how orangutans use tools to how we do.