A listener may readily take “lion” as a figure of courage. To use it for an unusual quality may require additional contextual information, but even an elaborate explanation does not automatically create a fine metaphor.
The ground of resemblance is the quality connecting the two sides; the contextual clue indicates that the literal referent is not meant in this particular use. An unsuitable resemblance and an insufficient clue are separate defects.
Showing that an actual animal is not intended does not, by itself, identify an unexpected feature that the audience has no reason to associate with a lion.