People are thinking of us humans as we are today but our ancesters of long ago began a sort of transition to humanoids in a temperate region, probably wandering about as gatherers where food was available all year round, more or less available by just picking it off trees and bushes. Why "work" for it when you can just pick it up?

The World has gone through many changes of climate and the humanoids expanded their range away from the most productive regions so eventually had to hunt as well as gather.

By expanding their range to where Winter was upon them, they'd either have to learn to store food or become hunters to eat meat.

As humans as we know us, we ate a mixture of fruit of all sorts and meat so there was no imposition on the human race to be vegetarian at any time.