Exactly what BlueBelle says.
My DGS now a teenager, would have reacted to an unexpected present ( at age 4/5/6) from a stranger ( sometimes even with a family member) in the same way.
He has autism.
Sometimes he refused to open presents at all, and when he did, he ripped the paper off and threw the presents aside.
That side of things improved with age, and now he opens presents, smiles, and says thank you.
When young, that would have been impossible for him.
He also sometimes shouted at me when out and about and had rages.He drew many dark looks and tut tutting from adults around.
So, you never know, and even if you ask your new friend about it, she may not know, or something may be undiagnosed as yet.Give the little boy the benefit of the doubt.