> how much better is water ? is it 100% clean ?

They did provide a reference point...

> if you got poop on your arm, maybe while changing a diaper, would you wipe it off with a piece of paper and consider it clean?

...were you expecting something more rigorous?

yes, I don't really understand the whole thing.

A bidet you use water to clean your outputs, instead of paper only. But

1) you probably have your arm under there to dry it too, it's cleaner but not perfectly clean I suppose. So you might have bacteria/microbes too

2) I forgot my 2 but you get the idea. Unless you have something that doesn't involve approaching your ass you're still not 100% clear.

It is infinitely better than dry toilet paper. Trust me because like OP I've used both methods and I am never more grossed out than after going through a North American toilet.