Meat-eaters for example mostly refuse to eat human meat, but choose to eat any other kind of meat that is pleasant--cannibalism excluded.
This standard is strict as well, there isn't any leniency allowed for cannibalism in the common day.
As for the suggestion that vegans are no more dedicated to their diet than anyone who does not eat human meat, I find that frankly bizarre. Refraining from cannibalism in a society where cannibalism is illegal is extremely different from avoiding all animal products in a society where animal products are nearly ubiquitous. People who don't eat other people are essentially going with the flow. (This is not to say that they would be cannibals in a different situation, just that few are even presented with the choice, and choice is an important distinction here.)
When I first heard it, I didn't like it because I thought it was based on the popular conception that vegans practically starve themselves. But having read more about it, I think the concepts are indeed similar.