I didn’t necessarily mean everything listed in the OP is correct. (I also wonder if his teachers really told him *all* those things.) But he threw in true things on his list. For example, Rav Chaim Kanievsky shlit”a writes in his Seforim to not step over a child. And spare us the drivel about the last few hundred years. If the Achronim tell us something (i.e. Eliyahu Hanavi at the Seder, women shouldn’t drink havdala wine [nothing to do with growing a beard though], etc.), they didn’t invent it. It comes from our Mesorah all the way back. Even if the earliest Sefer YOU found is “only within the last few hundred years”.
And even if another Achron disagrees with a certain concept, a teacher can teach something as a fact based on another valid source (i.e. an Achron) cites it as factual.