Lol!
Interesting point: is it prejudice to know about the "usual" prejudicial stereotypes that others might refer to, or buy into?
I was recently (last year) put into a position where I sounded prejudiced by never having heard of the "Black Lives Matter" movement, despite having millited for and generally supported the better sensitivity training of the police in my own country, as opposed to what goes on in the U.S. So, was I racist for not knowing a slogan from the neighbouring country? Despite knowing and working against the problem locally?
Apparently, I was. That's what happens when appearances matter more than stating the facts and acting accordingly.
Of course, this joke says it better, "pithier", than I do... although I'm sure this goes right over the heads of many people. (-1/2 star for being an obtuse court jester, i.e. for the lost opportunity to really push the conversation further through the humour.)