This is something that I feel that I need admit. I have hit a bird before. I was very young. (about 12) The bird bit me very hard on the ear and I batted it away without thinking. I felt horrible that I had hit the bird. Fast forward to now. I would never hit my keets. I am older (28) and I learned from my mistakes. My keets are spoiled rotten brats who nip me all the time. I know now that birds explore their world through their beaks and only bite when defending or grumpy.
I was a child reacting on instinct (pain)and I did something incredibly stupid. I did learn from my mistakes. And I went on to work with many birds and animals at a museum.
This is all I want to say on the issue. I am not here to start a huge blow up. I feel that the person came here with honesty. Hopefully they have learned. And yes it will take the bird a long time to build trust back.
When I stepped on Basil (accident) it took him almost 3 weeks before I could touch him. He just recently is getting to where he will land on the floor without freaking out.
It will take some time. Birds do remember. They are very wonderful and intelligent creatures.

RIP Peeps