One thing that will certainly be to your son's disadvantage is if you do anything that could get you put into the box labelled: "Difficult Parent Who Doesn't Understand Our Systems and Who Won't Learn German". If that happens to you, it will work out badly for him, now, and in the future.
Therefore, I'd recommend that you base your decisions on finding ways to work with, and not against, the teacher (and the rest of the powers that be, at the school), if at all possible.
Whatever it was that made you feel she was being rude to you... just remember that at least a part of it gets lost in translation, not only language wise, but also culturally. It is at least possible that she did not mean to be rude, and just as possible that she may have found something you did to be rude. Without your realising it.
So my advice would be to try to go beyond that and bridge the gap. Remember, in some sense, they are "your boss", and the best to do is tame them, win them over, etc.
I'd recommend taking the form back, and saying that you've now read up about the language support and are super impressed, and very grateful that Switzerland offers such a service for immigrant children, and (if this is true) that you doubt very much that your country of origin provides the same. Then say that you're glad your son has the opportunity, thank you, and that these and these other points on the form make sense to you, too.
Next, ask whether she could explain to you about the motor skills, and the drawing, since you had not thought there were deficits nor had, as far as you had understood, the doctor and the KITA. So now you are naturally a little concerned to learn that she thinks there are. Could she please give you examples of what she has observed, so you can understand better? Of course you are aware that we all behave differently in different settings, and so perhaps she is seeing something at school that you hadn't noticed at home Or vice versa (have a few of your son's drawings in your bag, in case you want to show her, once the atmosphere is more easy-going). Also, the KITA must have used a certain type of assessment, and the doctor perhaps another, and perhaps she yet another. That's why you'd really like to know, from her, please.
I can imagine that you might not like my suggestions, since you already feel she was rude to you, and you disagree with the entries on the form. However, schools here don't work according to any concept of consumer rights, and they do weild a lot of authority. Therefore, if you can nip any animosity, be it hers or yours, in the bud, and turn the relationship into one of cooperation and collaboration, you will be doing your son a great service.
Edit: I see now that Rufus said it so much more succinctly!