You asked for an official document, and I can't give that. But I will try to speak for the teacher here. I don't agree with deducting points, but want to point out that the strategy of identifying axb with b+b+...+b (a of them) may be useful for students.
Mathematics generalizes, but it is helpful if it starts with something concrete. If some of the kids think 5x3 means 5+5+5 and others think it means 3+3+3+3+3, then it may be hard for them to discuss the ideas with each other. If they all start from the same place, and are led to notice that these two different sorts of problems always end up with the same answer, then they get to discover commutativity, instead of having it forced on them. (What I remember of the 'new math' of the 60's is having to write "this is true because multiplication is commutative". Gag.)
[Some kids will already have thought about this, and will already feel that both are the same. It will be hard for those kids to be put back in a box. With my bad memory, I would never remember which way was "right". That's why they shouldn't have points deducted.]
My friend wrote a great couple of blog posts referencing this. His niece thought of multiplication this way. He later saw the classwork behind that. In the comments on that post, he and I discuss the merits of this approach.
Although my friend is in New York, the school he references at his blog turns out to be in Connecticut. For New York, on this site you can find: Common Core Learning Standard 3.OA.1: Interpret products of whole numbers, e.g., interpret 5 x 7 as the total number of objects in 5 groups of 7 objects each. For Connecticut, I'm not sure.