That’s a diet that’s avoiding nightshades not a vegan diet. Some people think nightshades can trigger inflammation or autoimmune diseases but there really isn’t any evidence about it. Some people with irritable bowel disease fine nightshades trigger flare ups but that’s about all I’ve heard of.
I’ve heard a saying, two things you should never do on the Internet are argue or explain. It takes up a lot of mental energy and time to do it for no reward.