It was brought up as possibly-true in my 1980s high school, so I guess it was probably something he learned in high school or college in the 1950s or 1960s and never unlearned. People forget that so much more of what we thought we knew before google, wikipedia, and snopes was wrong. You have to work harder to be wrong on stuff like that, nowadays, since it's so easy to look up. In 1991, you had to go to or have a decent library to find out that that was well-known to be wrong, so a non-specialist might never question what they learned in long-ago school. Now, it's so easy to look up minor details as you write an essay that it seems willful if someone doesn't, but if you apply that standard to twentieth century essays, you'll come away with a view of the writers that's often unwarranted...

Next up: spellcheck. ;)