intentional walk rules

Question
During the Oakland A's TV broadcast on 8/17, there was a trivia
question asking why the catcher put his throwing hand on his chest protector before or during (didn't have time to re-read it) catching the 4 pitches on an intentional walk. Any ideas?

Answer
Jeff,

There are no rules that would answer the question. After asking several fellow umpires, no one has a true reason on why. Several ideas were passed, but none could be agreed upon by everyone.

The closest rule that applies is the rule that states a catcher must remain in the catcher's box until the pitch is made. However, this doesn't apply to arms or hands, only the feet.

I would be interested in knowing what their answer was.