Whether or not a parent is 'thrilled' or otherwise by the behaviour of a 12-year old is somewhat different to whether or not the challenge to authority (as was the case here) is acceptable or not.
I am sure that even you, Floo, would have been angry in the first instance - most parents would, but would then - in a different way, and probably at a later date - have probably be pleased with one of your children had they challenged the interpretation of a law in an appropriate way at the age of 12.
I would still not be pleased if my kid of twelve had behaved in such an outrageous way, even if he had right on his side. I speak as one who has any extremely intelligent grandson, now nearly 14, who challenged his mother at the age of two to explain how she knew Jesus existed as she couldn't see, hear or feel him! Our lad would certainly have given Jesus a run for his money. On the occasions he has consented to go to church with his mother he has interrupted the sermon and challenged the preacher, very politely, on some point they had made with which he didn't agree, YE GODS! As you can imagine he doesn't get taken to church very often.
As the boy has Asperger's syndrome he thinks his behaviour is reasonable! Now there's a thought, I wonder if Jesus had Asperger's syndrome too, it appears he was intelligent; a lot of very bright people have Aspergers.