It is not normal behaviour for a kid that age to go wandering around eating out of garbage cans when they are stark naked, no matter what the circumstances.
I would guess that the kid had behavioural and/or mental issues. The mother was probably having to cope with an impossible situation without resources or adequate support, and taking the kid's clothes was her way of managing it. People do strange things under those circumstances.
It's normal if the child is hungry.
This isn't the only one case on this thread where the child was found eating out of trash cans.