Define "Smart"

I ran across this article about feral pigs in upstate New York via Ann Althouse.  But what struck me was this paragraph:

Last year, the state set a similar corral trap too soon, catching only three pigs. After that, none of the others returned to the area, even after the trap was dismantled. “I’ve never worked with an animal this smart,” Mr. Reed said.

So, if they're so smart, why didn't they return when the trap was removed?