Trifle Only skimmed so sorry if this has already been explained and I've missed it.
You're right, it is a semantic distinction between the behaviour or the child being labelled as naughty but it makes a big difference to how people (adults) interact with the child and manage the behaviour going forward.
If you call the behaviour naughty then it suggests the child can be taught to make better choices and better behaviour options. It's presumed that the child just hasn't learnt differently.
Labelling the child as naughty conveys the idea that it is part of their 'core personality' and just the way they are. Much in the way that they are blonde or brown eyed or whatever. It implies that it is a fixed and immoveable trait. The problem with this is that people then expect poor behaviour from the child, they are more likely to be looking to that child for poor behaviour and so 'see' it when they might not see it in others (less likely to give them the benefit of the doubt).
Tbh, we tend to avoid labelling the behaviour as 'naughty' too. Well I do. There is no doubt that some behaviour is 'unacceptable' because, even where a child has SN, it's not 'acceptable' that another child might be scared or hurt. And that means that we are more likely to look for an alternative explanation - undiagnosed SN, problems at home, low self esteem...
It's not actually about whether the child ever hears the words "you naughty boy" or not. It really is the attitude/opinion/belief held by the adults around them that is important. So yes, adults talking to each other and describing the child as 'naughty' is very much a problem.