Most teams don't shoot 75% from unguarded FT line.
The stat I see for NBA is around 39% for an unguarded 3pt shot. They don't break it down for home and away, but it is mathematically unlikely that a there is a huge difference like you suggest because 75% at home would require 3% on the road for unguarded 3's to get at a 39% combined average..
I would guess USC might be in the low 40's /high 30's for unguarded 3's with their best guys shooting at home. The fact that they were at 66% is partly bad luck and partly Fran's defense letting guys get into a streak of confidence. Everyone is more confident shooting after they see one go in.. Iowa defense is great at giving easy layups, opens 3's to let confidence streak build.