The Greeks and the Vikings (and many others) told stories about giants.
Here are two possibilities:
(1) They were telling stories about beings who - despite, in the stories, seeming by all accounts to be big humans - really were not big humans, but were some other sort of thing that the Greeks and Vikings and others knew nothing about and never tried to describe;
(2) They were telling stories about big humans, and not imagining the world of those big humans to be constrained by considerations (like the limits of human biology relative to size) that they didn't even know about.
I know which possibility I think produces a more coherent conception of imagination and storytelling.