The Vatican does not own the definition of the word *heresy*.
http://www.merriam-webster.com/dictionary/heresy
her·e·sy
1 a : adherence to a religious opinion contrary to church dogma
1 b : denial of a revealed truth by a baptized member of the Roman Catholic Church
1 c : an opinion or doctrine contrary to church dogma
2 a : dissent or deviation from a dominant theory, opinion, or practice
2 b : an opinion, doctrine, or practice contrary to the truth or to generally accepted beliefs or standards
If the RCC wants to declare people who deny their teachings as heretics against the Catholic church, then that’s their prerogative. However, they are in no position to declare them to be heretics against Christianity as a whole.
Thank you for proving my point that heresy can mean anything contrary to the Catholic Church.