What they're doing is good, giving him both "boy" and "girl" things and letting him choose which he likes or maybe both.
And
at all the people saying he needs to choose one or the other because "he needs identity"
Just because he wants to play with dolls and trucks instead just one or the other doesn't mean he has no identity. Seriously
As long as the parents aren't forcing him , there's nothing wrong with not imposing gender norms on a child. If he were to say, "I don't want to wear dresses and play with dolls" and they still made him that would be different.