I think the thing is Joanne, you have to ask yourself some questions...if I correct this person

will the world be a better place?

will I feel better?

do I care that they are wandering round talking crap?

will it be appreciated?

do we like each other enough for me to bother that my friend is making a fool of himself?

sometimes its a tough call. if you really like someone who has exposed their ignorance in front of a very well informed audience.