Your bird is doing what most bird do 'closet talking'
Mishka, my AG, spoke in the closet for about 7 weeks. I recorded him, knowing exactly what he was able to say. I then proceeded to add more words with the words he was saying.
He talks to me from inside his cage, on his playpen, play stand or his potty.
We train for an hour each night, him on my lap, sitting face to face (beak to nose)
Me chatting away, teaching him new words.
Only recently, about 3 weeks ago, he has opened up completely, repeating the words I am saying to me, face to beak.
I reckon they are shy in the beginning and are practicing.
The more a bird matures and gains confidence, only then will they will begin to open up and talk openly.
That is just my opinion....