Technically vegans are omnivores, too: being an omnivore means you are able to consume both plants and animals. Humans as a species are omnivores. Choosing to consume animal products is something else. I had always considered being an omnivore exclusive from being a vegan but I didn't have a good answer for lack of symmetry between a diet I am capable of eating and the diet I do eat. The "vegan" word for it is Carnism [1].
[1] https://en.wikipedia.org/wiki/Carnism