From what I understand buckwheat is actually a grass not a grain. I am allergic to gluten and instantly know when I consume it. Buckwheat has never bothered me. I also don't agree with his views on coconut oil or fruit. There are certain fruits that are definitely not good for AF, but I have found berries in particular to be beneficial. I don't like that he recommends corn either.
But there are always going to be recommendations that not everyone agrees with. All in all Wilson knows his stuff, but many say he has strayed a bit from the original teachings of Paul Eck.