They didn't panic at the WTC and they won't panic over this. There might be a crowd surge and some injuries from that, but panic is not in the cards.
They also weren't closed in at the WTC. In an indoor arena, I imagine some would panic. I wouldn't, nor apparently would you, but some likely would. But you may be right.
Let's just hope we don't have to find out.
The WTC had moderately well done escape plans, and I would assume that most who worked there had a general idea of what to do in the event of an emergency. Basketball stadiums have small exits, they are not always well lit in the stands, and there are a lot of people who are at them who are unfamiliar with their surroundings. A bomb goes off, people run to the exits, others go off.. they panic. Look at what has happened at sporting events overseas with stampedes.