There is an actual agreed on definition of veganism by vegans, created by the vegan society who created veganism and coined the term vegan to describe themselves

Sorry, but that is just not how language works. One group does not get to define a term and insist everyone else uses it in the precise way they do. Words’ meanings are defined by how they are used. And the term vegan is used in the way I described all the time.

A word’s meaning can also change over time. Even if you were correct that the term was coined to be an ethical standpoint, that would not preclude it later evolving to have the broader meaning it does in today’s society. That would be the etymological fallacy. But in fact you are not correct about that either. The term was coined by Donald Watson and Dorothy Morgan, because they wanted a more concise term for non-dairy vegetarians. The first time the term had caught on in the wider public enough to make it into a dictionary, the agreed meaning of vegan was “a vegetarian who eats no butter, eggs, cheese, or milk”. You can thus talk about ethical veganism (which seems to be the only subtype of veganism your definition would accept), environmental veganism, or dietary veganism.