The warning is specifically for trans folk.
The government’s website issued guidance for transgender travelers, saying that U.S. ESTA and visa application forms require travelers to declare their sex, which should reflect their biological sex at birth. Travelers with an “X” marker on their passport or whose gender differs from the one assigned at birth are advised to contact the U.S. Embassy in Dublin for further information on specific entry requirements.
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.