I'm going take a wild swing here and say it was one of those 'live capture' traps. I'm surprised you found the little guy alive. The one and only time I tried that, the mouse was very literally scared sh**less - then died, probably of a heart attack. It was really disgusting and I felt awful.
Even though this area of central NJ is about as suburban as you can get (green space. Um, sure, we got some of that), I think the mice are more of the country variety. You know, chewing on a long stalk of hay with a tiny corn cob pipe. They're not like those big city mice. When THEY get . . . arrested, they just ask for their lawyer and chill.