As most people know, vegans avoid animal products as much as possible, not only in their diet: veganism is not only about food.
The term 'dietary vegan' has been used at least on one occasion, on one page of the site of a vegan organization.
I've also used the term myself, in the past, to distinguish between vegans and people who live on a plant based diet. Then I realized that if I use the term 'dietary vegan' to describe people who eat vegan food, but are not really vegans (they may eg. be hunters), I just achive the opposite effect of what I want.
Because I give the impression that there are two kinds of vegans, which again gives the impression that the vegans who are not a vegans are also vegans.... .
Let me explain:
When people add the word 'dietary' before the vegan, it is because they know that even if you are living on a plant based diet, you don't need to be a vegan. If vegan would mean 'living on a plant based diet', there would be no need to call someone a 'dietary vegan', right? If 'vegan' only was about diet, the word 'dietary' wouldn't need to be there at all. The word 'dietary' is added because vegan is not only about diet.
So the intention behind using the term 'dietary vegan' was good. But it has a built in, negative, side effect. It creates an idea that both vegans and dietary vegans (who are not vegans) are vegans.
If 'dietary vegans' are vegans too (which users of of the expression 'dietary vegan' obviously didn't mean, since he added the word 'dietary'), at some point some people will use the word vegan about people who eat plant based food, but who might go hunting in the weekends.
So, while I, and everybody else who knows a little about the history of veganism, agree that 'vegan' is NOT only about diet, let's not attack vegan newbies for misusing the word 'vegan'. It's better to contact that organization, and try to discuss the situation with them.
Are there people in that organization who want to change the meaning of 'vegan' to something else that it has always meant? I don't think or hope so. Therefore, IMO it would be a lot better to avoid the term 'dietary vegan', because it can create the idea that there are two kinds of vegans, which again in the future will mean that the word vegan can be used about people who don't fit with the original and - by far - the most common used definition of the word.
We had a poll in 'Veganforum 1', which showed that less than 1 out of 10 used the word 'vegan' about someone who was living on a plant based diet only, which confirms that the original meaning of the word is well known and used. I'm originally from a small town in a small country without any vegan organizations at all, and even in that little town, many years ago, people knew that veganism was about more than food, it was about respect for animals.
Let's not change that.