He does this shyt constantly where he projects his ignorance on everyone else.
Literally EVERYONE who talks about the 1619 project knows that its about slavery. The fact that he thinks they don't know it's about slavery just shows how fukking ignorant he is about the project. He didn't know that, so he expresses that by claiming that they're the ones who didn't know it.
Just like when he said Kaep and company didn't know that they were protesting against police brutality. THEY knew what the protests were about. He didn't, so he projected and claimed that they didn't.
There have been literally dozens of examples of that, "No one had ever heard of Juneteenth", etc. Every time he exposes his ignorance, he claims that it was everyone else who didn't know.