I would give him some more time to get used to you. Birds get very settled in there ways and when they experience change, it could be a little uneasy for the bird. Just have some patience and he will eventually come around. It was very nice of you to give him a good home. Good luck!
Seconded!
Patience will definitely help, and - by working with the bird - will allow it to trust more easily, but it does take a while...
Stick training, as said by friedsoup, will definitely help!
And it's cool there are people who are able to take in birds, but it's horrible people are losing their jobs or other things that result in having to give up their pets. It's inhumane...
I took in a blue crown, who was abandoned in a pet store bathroom. The pet store did a good job with what resources they had, but it was clear the poor bird - who bit at every opportunity - had been neglected for a long time. Tybbi no longer bites, and has learned I'm an okay guy. But it did take her a couple of months for her to drop her defenses.)
Tybbi used to scream, but with time and temperament, she would later mimic her previous owner's alarm clock right at ~6AM. Now she greets me with "Hi, Dave!" when I wake up. I suspect she understands the context, as she sometimes says "How are you?" (but in a less recognizable cadence as she learned that phrase from me) after I acknowledge her "hi" greeting. It's possible the previous owner may have been a "Dave", but between finding out about Tybbi and acquiring him, it was one day. She could not have learned "Hi Dave!" from anyone at the pet store in that period of time...
The vet found Tybbi was malnourished, but has responded well to Zupreem pellets and real carrots (vitamin A deficiency also being prominent regarding her beak peeling).
The vet, who has worked with parrots for two decades, thought Tybbi was 5~6 years old due to the condition of her talons. Two of my GCCs are that old and their feet have the scaly description the vet said. Tybbi's feel more supple, but a blue crown is not a GCC. It'd be fun to think Tybbi is but two years old, but reality suggests going by the vet's prognosis is the more rational course of action.
I do have 3 other parrots - Rusty and Scooter, cagemates from a different pet store, and Rosie (abused in a pet store and purchased just to get her out of that creepy dump). None of them interacts with the others, due to territorial issues... and Rosie will go out of her way to attack Rusty.