To be fair to the dude, I didn't know this either until a teacher taught by teaching us about peanuts. How many of us know much about most of the things we eat?
I grew fennel last year. Have been eating fennel for years and thought we were eating the root part (the white part) and that the green part was the above ground part. No. There is a root underground but the whole fennel sits on top of the soil looking like it will tip over any minute. The white and green parts.
I know food, have worked at groceries, in restaurants, health food stores, I cook. But gardening has taught me new things, and I'm over 50.