You cant have a copyright on a tune.
A song can be copyrighted and creating a new song with a tune from an existing song would be a derivative work and creation of derivative works is a right of the copyright holder.
Think about when you go to a wedding and they play the latest hits is it legal?
This is a different issue. performing rights only apple to public performances. A wedding is a private event.
Did they even sell it?
Yes, but that is irrelevent.