Maybe he's got an upcoming project, maybe not. I have been attending these type of shows for many years. It's a great way for fans to meet and share a few moments with different celebrities. I have met many actors other the years: Angie Dickinson, Robert Conrad, Samantha Fox, George Hamilton, Carol Lynley, to name a few. The autograph and picture serve as great mementos.
Generally, the celebrities who appear at these shows are no A list anymore. The exception would be Comic Con, where Sylvester Stallone and the like were charging what I considered to be an outrageous amount of money, $485.
The Batman and Star Trek casts have been on the autograph circuit for many years. It definitely strokes their egos and mskes them feel like they are A list again, even just for the duration of the show. Plus, the transactions are all done in cash. How much of that is reported as income is between them and the IRS.