While the guy is obviously the one out of his mind to say such things about people with a minhag different to his own, the truth is that here the OP has also made a slight mistake.
There is no such thing is a minhag not to say hallel on pesach night. Yes, Ashkenaz do not have the minhag to say hallel on Pesach night. But they do not have a minhag not to say it! There’s a big difference. And Gedolei Ashkenaz have paskened that because of this, that if an Ashkenaz person davens in a shul where they say hallel, he should say it and not be poresh from the tzibbur by going out early, because nobody has a minhag NOT to say hallel on Pesach night.