So it’s made of shit, right? And shit is an animal product. But barring a night of drinking or a particularly aggressive burrito, shitting does not harm the shitter; it’s beneficial and required. Also the animals in question can and do consent, does that make it vegan?
[off topic?]
The Ophiuchi Hotline by John Varley. Great science fiction novel. It comes to mind because the protagonist is a scientist who was arrested for using human DNA for flavoring her bananameat trees.