I'm sorry OP, I realise that someone who has ADHD, or is a parent of a child with ADHD is likely to have an emotional response to anything that implies that it may be their fault, so sensitivity in discussing this is needed.
I don't feel the JW states that certain foods cause ADHD. His actual words state that his personal experience is that his, and children's behaviour in general is affected by a heavily sugar-laden diet, and that he passionately feels, and indeed research backs up, that people, especially children, can improve behaviour and concentration and mitigate the symptoms of ADHD, and potentially avoid being medicated by adopting a good diet. This shouldn't offend anyone, if anything people might be encouraged by his story and research showing that small changes can have a big impact.
There are a couple of things that wind me up about Joe Wicks, I'm not a fan of all that 'midget tree' talk etc., but that's on me, I have a low annoyance threshold. I also feel that he implies his incredible physique is down to a few jumping jacks and burpees, he clearly lifts heavy and eats a lot more than his cookbook meals. But he's a force for good in the world, and people that hate his message are quite possibly in denial and making excuses for their own inaction.