Mostly they're dried, including pod, the rest is genetics.

They are botanically nuts, though: They are indehiscent, meaning they do not open to release their seeds. They're also fruit. It's e.g. pine nuts which aren't nuts because pine cones do indeed open and release the seeds. Of which you should roast a couple and mush up with a wee bit of garlic, a metric pound of basil, some salt, some proper hard cheese, and quantum satis good olive oil. Use a mortar the basil wants to get squeezed, pre-chop everything or you're going to be there forever. Throw your pasta, shape is not that important as long as it's bronze-cut, into a pan at lowish heat, put your pesto on top, add some of that pasta water (incl. the starch in there), the saponids in the garlic will help with emulsifying everything. Reduce very carefully you don't want to denature the cheese.

I guess making a distinction, in the culinary context, between nuts and peanuts makes sense because allergy considerations, legumes are a class of their own there.