The term suggests that the person not only follows a vegan lifestyle, but also cares about the aesthetics and social status associated with veganism. A "veganista" might be someone who dresses in the latest vegan-friendly clothing, uses high-end vegan beauty products, frequents trendy vegan restaurants, and shares their vegan lifestyle on social media.
The term emphasizes the intersection of veganism and fashion/lifestyle, implying that being vegan can be part of a person's overall curated image and social identity, not just a dietary choice. It reflects the growing mainstream appeal and "trendiness" of veganism in recent years.