Can mean a few things but "chicken scratching" is normal behaviour for greys.
What Google says
Chicken Scratching: African Grey Parrots will "chicken scratch" at the bottom of their cage or on the carpet. This is a normal behavior for them as in the wild, they do this to loosen dirt and mud.
1. he wants to get out of the cage,
2. he is hungry so trying to forage,
3. Wants attention or its just normal behaviour.
My african grey does this even when he has been out of his cage for hours playing with me on the couch. He will be playing with a toy and the next moment just bite on the couch and start scratching like a crazy chicken