Y’know, that’s an interesting point.
I blame our nutritional education. I grew up with the Food Pyramid (now debunked), and peanut butter would be considered a “meat alternative” which I think people conflate with being a source of protein.
That’s not how it was taught. Maybe that’s how you learned it. Peanut butter and peanuts were on the bottom row with vegetables, not a meat sub.
https://peanut-institute.com/wp-content/uploads/2017/08/pyramid-med.jpg
Your food guide looks different than mine. Notably, yours has a distinction between meat, poultry, and seafood where mine are all lumped in as one category that also includes legumes.
For what it’s worth, I believe this guide has been fully discredited. There was a considerable amount of lobbying to present certain foods prominently.