I don't think anyone has claimed that there are no restrictions on freedom of speech in Austria (or elsewhere, for that matter).
I'm not convinced that it is right or wise of Austria (and Germany) to outlaw Holocaust denial, but I have no sympathy for Irving. He is a pro-Nazi liar who was exposed in court in London when he sued a historian for calling him a Holocaust denier. He also knew perfectly well, when he made Holocaust-denying speeches in Austria, that he was breaking the law and risked prosecution and imprisonment.