Your viewpoint is as speculative as mine, as the fruit and vegetation before the flood grew greatly and was watered from below the ground, all various kinds of edible fruits and nuts and plants were in abundance and nobody would have needed to eat meat.
However, whether some did or didn’t, what is fact is that permission for peole to eat animals was not given until after the Flood, and the fear of man was not placed in animals until after the Flood.
It is a crucial point to the credibility of omnivore diets vs. vegetarian to note that disobedience was the norm — in fact meat may have been viewed not just as something nice but as an overtly pagan act.