Sponge bath, maybe some kind of disinfectant like the quick drying alcohol cleaner or some sort of wash-less foaming soap. Moving on to the point, there could be several reasons why you wash your hands after going to the bathroom. Some of them probably date back before that study was done. However, we can come up with some legit reasons as to keep doing it.
-How many times do you just go into the bathroom to 'only' wash your hands? Two birds with one stone, the sink is already next to the toilet so why not do both? This allows us to go onto other reasons, as it allows for the washing of the hands after the break.
-Even though your privates are relatively clean, doesn't mean everyone's are or it's a hot day with nice bit of sweat going on day there

, after using the handle or opening the door germs are sure to be latching on to you.
-It's comforting to other people to know you just had a nice bm that you're hand didn't slip or something and you not do anything about it.
-Plus, I'd say the one of the biggest reasons is because unless you've got open wounds around where you are handling it doesn't matter if a few germs hang out around your privates. However, your hands will go to your face, eyes, and mouth(food/yawn/pick your teeth).
So it makes sense to wash your hands as opposed to your clean privates.