Green beans and dry beans are somewhat interchangeable and somewhat different.
Green beans produce seeds. If the pods are allowed to mature they will eventually dry down and can be harvested and used like dry beans.
Dry beans often have very fibrous pods that are too tough to want to eat as green beans. Perhaps if they are very tiny they can be used as green beans, but even then many of them are too fibrous to be palatable.
Agriculturally green beans have been selected to grow pods quickly and then take a long time to mature. That keeps them at a good eating stage for a longer time.
Dry beans have been selected to mature quickly. Dry beans have also been selected so that the pods separate more easily from the seeds during threshing.
Green beans have been selected to continue making beans for an extended harvest. Many dry beans have been selected to mature their whole crop all at once and then die so that the whole plant can be harvested at the same time.
Green beans for canning have been selected for white seeds so that they don't stain the cooking
water.
Dry beans have often been selected for the taste and texture of the cooked seeds. That work typically hasn't been done for green beans used as dry beans, so the flavor or texture can be a bit on the wild side.
Some beans are dual purpose. I think that I'd put Rattlesnake into that category. I think that protein levels of dried seed would be about the same between varieties. Green beans are mostly water, so in comparison to dry beans they are not a great protein source.
Here's some bean photos:
The top left bowl contains runner beans. They are edible as snap beans, as shellies, and as dry beans. As snap beans and dry beans they are a bit coarse. A marketing person would describe them as robust. They make wonderful shelly beans. A shelly is taken out of the pod about the time the seed matures, but before it starts drying down.
The top middle bowl contains traditional dry bean varieties. None of these pods are edible as green beans.
The top right bowl contains edible pod bean seeds. They remain tender till the pods get quite mature. There is a Rattlesnake bean seed in that bowl.
The bottom left bowl contains Tepary Beans. They are inedible as green beans, due to poisonous tasting pods. They cook up fine as dry beans.
The bottom right bowl contains beans that are tender or tough as green beans. Some of the seeds don't absorb water readily, so they are not real useful as dry beans either. This one is a breeding
project in progress, so that's to be expected.