Something like this happened in Oakland last month as well. One of the rookies, Matt Carson, hit his first home run. So naturally the team tried to exchange the ball for the usual stuff - an autographed baseball by Carson a perhaps a bat.
The guy who caught it? He said no deal, pay him $10,000 for the ball. Carson, being a rookie, decided the bat he used would suffice by itself and saved himself the trouble and a bunch of cash that, being a rookie, he did not have.