Overrun First on BOB

[tibear]

I know this has been asked many times already and in OBR the batter/runner is entitled to overrun first without liability to be put on, as long as no attempt for second.

Had the following question on umpire quiz with OBR rules:

The leadoff man walks. After ball four, the catcher returns the ball to the pitcher who starts walking around the mound in disgust. Meanwhile the runner reaches first and then walks off the base a few steps, bends to pull up his socks. The pitcher then fires to the first baseman who tags the runner. Is the runner out?

I said no, the answer key said yes and the clinician said the BOB was an award so that meant that the runner was entitled to first and nothing more.

As indicated earlier, I've found many earlier threads which indicate the runner is save but would like rule references to send to the clinician.

Thanks