Your dragon is your Guardian, he protects you, he wouldn't have kept it secret for any reason. Its way simpler if you didn't know for story purposes but practically doesn't change much, since the other Elementals will only tell your character like "The other Elementals quickly told me about the situation. It was extremely overwhelming and didn't sink in yet but one thing I did understand: They were surely responsible for the death of my parents. They will die." Not exactly like this, but no one actually has to say "You know Phil, there's Vygorns who are aliens which look like people bla bla bla" So just imagine they explained it to you. After you arrive to Nature's Haven.