I think that someone is being a little silly and saying that because one vegetarian did not eat grains, etc. it is necessary to define it as optional. I think that this is wrong, because:
Nobody claims that nuts and grains are not vegetable.
I have not heard anyone claim that a diet of nuts and seeds is non-vegetarian.
If we include this we would have to add lots of other exclusions, for example many Jains don't eat root vegetables, some Hindu groups avoid "hot" ([[Guna|rajistic]) foods such as chili, pepper, mustard, etc. 
I will restore your edit.