Matt,
I believe that you still get steam in a pressure cooker when cooking with oil. The moister in the frying food is escaping. With a tightly closed vessel the steam is still trapped and the heat is more intense than just cooking in an open pan. It’s been so long ago, 1967 to be exact when I tried to fry chicken in a PC that I really don’t remember exactly how much oil I used, but somehow I’m visualizing that is was about 1/2’” above the top of the chicken pieces. Anyway, it was nasty! And I already knew how to fry chicken well on the stove, and would just have the oil halfway up the sides of thee chicken, which works fine when you can turn the pieces over.
Eddie