The potato plant is a nightshade, closely related to the tomato. All nightshades contain poisonous alkaloids, including small amounts in tomato fruits and green potato skins.
The potato is still a vegetable though... Vegetable is a culinary term and can apply to any part of a plant, including roots and tubers.
Just to throw in another option: A blender, nuts, barista oat milk (it’s sweeter and less oaty), some fresh fruit or frozen berries, and some kale.
Takes about 3 minutes, you can experiment with different fruit and nut combinations, and some fresh kale means you’re getting some greens.
My go to is a big handful of peanuts, half a handful each of walnuts and hazelnuts, a cup or two of frozen raspberries, 2 or 3 leaves of green curly kale, a scoop of creatine, and enough oat milk for it to give it a good consistency - usually makes about a litre.