> Formal logic usually isn’t taught in high school
Have things changed? Last century, this was a key part of (in the US) high school geometry courses. I won't argue that it was as in depth as you'd get in a college course (like you'd be exposed to in a math or philosophy degree program), but it was formal logic and it was taught.
Not in geometry for me, but it was required in my linear algebra, discrete math and computer architecture classes, all of which were required for my CS degree.
I've found that any time you try to generalize about what is or isn't "usually" required in school, there are a lot of exceptions, to say the least. Curriculum is all over the place.
I would say high school geometry is still mostly "syllogistic" and not the formal philosophical / mathematical logic worked out between Kant and Gödel which forms the backbone of modern mathematics. It is good solid logical thinking, and mathematically correct! - but not really what the author means here.