I think by the definition of cultural appropriation, this clearly is appropriate example. Religions are cultural inventions, like anything else, like clothing. If Selena Gomez can face a twitter storm for culturally appropriating Indian garb and a bindi spot on her forehead in an awards show performance, I don’t know why religions should be exempt from the same charge.
I do not think Hinduism or any of the others are monolithic and did not mean to imply that in anyway. But they are NOT vegan. Veganism is a totally different philosophy and a social justice movement. Like Aneela pointed out above, she did not know what veganism was until she came to the US. We do not learn what veganism is through our Hinduism, or Buddhism or even Jainism. You will have to twist and manipulate those religions to ‘make’ them into veganism, and it cannot be done.