That may be a fair critique. Should SQL be successful only to mathematicians and computer scientists? (Who else would even know about set theory or Venn a priori?)
In my underfunded rural American elementary school, they taught us Venn diagrams. Not set theory per-se, but they taught us to read and create Venn diagrams.
I don't know if that's representative, but my gut instinct is that Venn diagrams are very accessible to the general public.
I do know at this point that he is technically right... But being 100% correct doesn't really matter at the beginning.
And Venn diagrams are right enough to start working with joins