Actually, I disagree with these other reviews. I think Harry not only acted appropriately in his anger; I think it was wrong for him to have to apologize. Luna disregarded his safety and risked exposing his true identity all so that she could satisfy her curiosity and to play a prank (something they haven't really shown a habit of doing).
Luna has heard all the horror stories about the tournament. She knows they are to keep Harry's true identity secret as well as the secret about their bond. So, entering him into a tournament where his life is in danger and where his life will be scrutinized by the press is not showing any consideration on her part.
Harry has every right to be angry and every right to break their bond since she place so little importance on him. She only thought of herself in doing what she did.
Harry had every right to be angry, but he didn't have the right to cruel to Luna (just as she didn't have the right to endanger him). So they both had to apologize to each other.
Thanks for the comments.