I'm an MD. I don't remember this specific piece of information being mentioned during my training. However, all the information need to reason about it was included...
What really blows my mind is how many people get it wrong, including my colleagues and especially dietitians ("they had one job").
"It is difficult to get a man to understand something, when his salary depends upon his not understanding it."
That is fairly astounding... I'm a paramedic and while I don't recall talking about this specifically, the answer was immediately obvious from the (comparatively limited) amount of A&P training we receive.
It's only Hydrogen... But it still needs to go somewhere. Oxygen comes in to carry away the Hydrogen as water--you can't urinate Hydrogen.