The phrase "like a lion with excellent table manners" is an example of a simile, which is a type of figurative language that compares two things using "like" or "as." In this case, the simile is comparing Bryant's devouring of the moment to the way a lion might eat its prey, but with the added descriptor of "excellent table manners."
The simile is using a lion to represent an animal that is powerful, confident, and skillful in its hunting and eating habits. However, it also adds the idea that the lion has good table manners, which is a humorous and unexpected twist on the comparison. The phrase creates a vivid image in the reader's mind of Bryant devouring the moment with confidence and grace, but without being too aggressive or uncivilized, like a lion that knows how to behave at the dinner table.