Not so much cleverness on the mouse's part as it is a failure on the trap-builder.

The mouse has to eat everyday, but you only have to catch him once.

Yeah that was a pretty bad trap. Sure the mouse was "careful" in getting his reward, but to be honest that food at least needed to be up higher in that particular setup. But, I think there happens to be too much weight holding that clothes pin in place; they definitely need to balance the weight far finer, so that even a very, very small movement or tug can collapse the setup.

Or you could at the very least make sure the rope covered all four sides of the food (though, again it should have been slightly more out of reach--it was practically right in the mouse's hands which defeated the purpose of the entire design).

I was kinda hoping it would kick the peg out after it was outside just to really screw with the trapper.