Food is one of those things which cause many frustrations for everyone involved. I definitely subscribe to the 'not making mealtimes a battleground' ethos BUT when faced with years of food issues even the most saintly can get frustrated and occasionally confrontational about food.
DS1 ate everything put in front of him until he was 9. At that point I cooked a 2 course dinner for up to 10 children who mostly ate what I gave them without fuss.
Then he started saying he didn't like foods he had previously eaten and would pick out stuff at first but eat the rest. Then he started refusing to eat certain foods mostly blaming the smell or texture rather than the taste. Since then he has never eaten potatoes (in any form), any cooked vegetables, any meat except chicken and sausages. He wouldn't eat anything in a sauce, ate pasta with a sprinkling of cheese. I can't say I wasn't frustrated, and, hand on heart, there were times that I tried to make him try something else. By the time he was 12 his diet was severely restricted so I decided I would only make him food that he asked for. It was a weight off my shoulders and definitely reduced the stress around mealtimes. I would simply cook for the rest of us and then give him a plate of raw veg, chicken or hummus, a wrap or pitta bread, and I never commented on his choices. By the time he was 14 he just sorted his own food out.
He's 24 now and, in comparison to his brother who eats anything and everything, still has a restricted diet. But he survived uni cooking for himself and now he's back home I've noticed more and more things creeping into his diet. He enjoys meatballs, burgers, chicken. He makes himself elaborate Asian dishes, enjoys Italian food and eats out regularly with his friends. He still won't eat any cooked vegetables but will eat all of them raw, never chooses to eat fruit although will eat a satsuma type citrus if I give him one.
One of the other children I fed (was childminding) once hid under a table and sobbed for hours because I put peas on his plate, he found mealtimes extremely stressful because he felt under pressure. He's 26 now and said to me on Saturday 'bet you never thought I would be a vegetarian eh' lol.
So my advice is step back. Take food discussions off the table and just leave him to it. You will all be happier for it.