You seem to be operating under the misconception that rudeness is only established by the response of the person toward whom it is targeted. Rudeness is independent of that factor. Spitting in someone’s face in my city is rude, regardless of whether the target thought it was or not.
Certainly I think there are things which are objectively rude. However even spitting in face might not be rude in every situation for example a dry spit in a play by actors portraying an insult would not regarded as rude because of the context and events surrounding it.
Not every action which is thought to be rude is objectively rude in every situation. For example public nudity is rude, but a man might find himself naked in public because his clothes were stolen from him. It would be clear whether he intended to be rude or not by the nuances of his behaviour.
The rudeness in this case is obvious, and its nature can even be determined: not to respond positively to effort that someone else has spent. Giving the child the doll was morally permissible, the doll is morally neutral, and the child was ungrateful and rude by not responding with charity or courtesy to the giver. Whether he cares or not is irrelevant.
Furthermore, placing that constraint on rudeness is nonsensical when you turn that position on itself: say that the girl had said thank you politely and the uncle considered it rude, or I look at someone and they consider it rude. No one in their right mind would claim that I was being rude, which suggests that the response of the alleged target does not factor in.
Giving a discalced nun a pair of shoes would be rude and worthy of rebuke. Perhaps the Uncle was being rude. Knowing the inclination of his niece to disavow material things he may have been seeking to tempt her to an attachment to worldly things by giving her a beautiful doll. In which case a retort by the child would have been warranted. This is what I mean. There are nuances to the situation, the way the child spoke, the way the child expected the Uncle to react, the way that the Uncle did react; which can often be lost in a quick relating of the story in the text of a pamphlet.
Our Lord said to a woman who asked for devils to be exorcised from her daughter. “It is not suitable to take the bread from the children and give it to dogs”
This was on account of the woman being a pagan Caananite. Now you would probably regard this as being objectively rude. But as our Lord cannot be rude we must give him the benefit of the doubt that there are nuances to the situation and the way he spoke to her which have been lost in translation. Here is what our Lord was most likely saying according to Barnes commentary.
“You are a Gentile; I am a Jew. The Jews call themselves children of God. You they vilify and abuse, calling you a dog. Are you willing to receive of a Jew, then, a favor? Are you willing to submit to these appellations to receive a favor of one of that nation, and to acknowledge your dependence on a people that so despise you?”
Now this nuance would have been very obvious to the woman who understand the culture of the day, but to us it comes across as incredibly rude.