Why does Updike in "Ex-basketball Player" write that Flick's "hands were like wild birds" ?John Updike's "Ex-Basketball Player"

In the third stanza of "Ex-Basketball Player," by John Updike, the poet uses the simile, "His hands were like wild birds" to convey the incredible swiftness Flick Webb had when he played basketball.  While conveying the speed and nervous energy that Flick has possessed, Updike's poetic image is in sharp contrast to the next line that describes the banal acitivites now of Flick's hands:

He never learned a trade, he just sells gas,/Checks oil, and changes flats....

Having graduated, John does no other than simple, monotonous activities with this hands;  he "just sells gas," and he "Checks oil, and changes flats."  These contrasting images of Flick's hands exemplify the controlling metaphor of the poem: The once great, stellar player on the basketball team is no longer free and unique;he merely engages in banal and trivial activities:  he pumps gas and checks the oil and changes tires.  No longer do crowds shout for him, no longer do they applaud.