The books "The Millionaire Next Door" and "The Millionaire Mind"

have chapters describing how the American millionaires, statistically of course,
teach their kids. One key was to give the kids some "armor plates" to defend
against negativities.

Your dad's response to the teacher might be intuitive, but essentially achieved a similar goal.
Your dad's courageous, too. Among all virtues, courage is what we need most.