Reversing gear pump rotation in hydraulics is like "Hello World!" in programming. It's one of the first "real" things that you learn in a hydraulic shop.
This... I wouldn't call it a mistake, but rather a very common scene, or an incident, if you will - happens all the time. I've seen it, and I have done it! It's really fun to look at and it's not so fun to experience - but it's also relatively harmless, and since it's so common I think it must be documented!
The incident is called - "Caramba, my eyes!"
It usually happens to people who are initiated into gear pumps. When you assemble a gear pump, especially when you reverse its rotation, a small amount of oil in the bottom bushing will "geyser" up through the hole in the driven gear when you drop it in place. Dropping a shaft in place is a very natural movement, as well as looking down the afore mentioned hole while doing it - which results in a perfect "My eye, my beautiful eye!!!" every time (as the jet of oil hits your unprotected eyeball)!
I can only promise you that the foggy vision will dissipate in a couple of hours.