You may touch sand with a club you have in your hand when you are about to lay that extra club down in the hazard. The penalty comes into the picture once you touch the ground with the club you are going to use to make your next stroke.
This may result in quite nasty situations when having two clubs in your hands and laying one of them down touching the ground (accidentally) with both of them. How would you rule that?
Yes, I agree in principle with your first two sentences but the book only refers to laying a club down and makes no reference to the club with which you intend to make your next stroke.
If you were intending to lay both down but did it rather awkwardly, I see no problem.
If he had one in each hand and one was not going to be laid down then unfortunately I see no way out of 13-4a.