That was a young person, so it may be that he actually never heard of Moses. Especially when media sources are so fragmented now. His choices of friends and media may have prevented him from learning that.
I guess he knows now.
I'm finding more and more often that people seem to not know things that I thought everyone knew. I think it's because of "information silos" where people don't seek out other sources of information and miss things.
In school, they used to teach certain classic areas of knowledge in history and literature, but now they don't do that any more. Also, young people, who may be in those "silos" may not realize the scope of what they don't know.