In moral philosophy, actions are often classified into one of four categories: prohibited, permissible, obligatory, and supererogatory. These categories can be defined in terms of each other. To say that something is prohibited is to say that it is wrong and that we are obligated not to do it. To say that it is permissible is to say that it is not prohibited. To say that something is obligatory is to say that it would be wrong not to do it. And to say that something is supererogatory is to say that it is not obligatory, but it is better to do it than to not do it.
Supererogation is the one that often trips people up. We all get things like “you must do x” or “you must not do y,” and even “you’re allowed to do z, but you don’t have to.” But it can be confusing for some people to understand “it’s better to do x than y or z, but you don’t have to do any of them.” The whole concept is controversial, and not everyone believes that there is such a thing as a supererogatory act. But those who do would tell us that it helps make sense of cases where we make a moral decision for ourselves and think that we’ve made the best decision without thinking that everyone else ought to do the same.
The loudest vegans—and the ones we are probably the most familiar with—tend to present veganism as a moral obligation. But the chef’s actions make perfect sense if we consider the possibility that she thinks veganism is supererogatory. If it is better to be vegan, but permissible not to be, then there’s nothing wrong with handling raw meat and preparing it for others to eat. You can give to charity without judging everyone who does not. You can help an old lady across the street without condemning everyone else walking by. And you can refrain from using animal products without believing that everyone who eats meat or wears leather is a monster.
On a separate note: sometimes morality is aspirational. That is, sometimes it represents a goal to strive for rather than a state that we must occupy at all times. To the extent that any particular moral commitment is aspirational, occasionally failing to uphold it—whether accidentally or otherwise—does not necessarily undermine our devotion to the ideal.