The excerpt from the article is odd. It states that Walz's position is that "the holocaust should not be taught as unique, but used to help students identify clear patterns with other historical genocides."
Weird dichotomy. I think it's generally accepted that every genocide is "unique." But when teaching about genocides (pretty heavy stuff for a high school level history class), I'm sure it's useful to categorize compare/contrast elements. It's hard to tell (based on the excerpt) whether Walz was trivializing the holocaust or just saying something like "here's the common recipe we see in genocides: [(1) racial strife; (2) coming off the heels of losing an international conflict; (3) authoritarian leader, etc.]".
That kind of lesson ("here's the common elements of genocides, (including the holocaust)...") seems more likely to me rather than him actually teaching about the holocaust, but somehow downplaying it or saying it's not a big deal or whatever.