It’s not unrelated actually, there is some tissue inside the nose cavity that is similar to the erectile tissue of the penis. That’s why the nose gets “stuffy” from sildenafil, and that’s why you sometimes sneeze when aroused.
A curious question, is nasal congestion has any correlation with high blood pressure?
I wouldn’t know. Sildenafil lowers the blood pressure, so I would expect the negative correlation.
I think it's vascular dilatation, it creates an effect similar to an inflammation : inflated, red, tissue
See also levomethamphetamine, the mirror image of meth found commonly in drugstores in Vick’s inhalers, acting as a vasoconstrictor