Technically, a category error means putting something in the wrong category or, according to Wikepidia, '...a semantic or ontological error by which a property is ascribed to a thing that could not possibly have that property.' But there might be a slightly greyer kind of category error. For instance, 'dance' (as a category): we all know what this means... but what we know might not be true of both, say, tango and ballet. Similarly, within 'tango' (as a category) there can be mistaken assumptions, so perhaps this is a sub-category error.
Last night I was talking to a friend who'd just taken a workshop with a couple of well-liked local teachers, who said she was puzzled that an Argentine teacher had told her to keep her shoulders steady, while the local couple asked why everyone kept their shoulders so rigid. & I remembered a class with Oscar Casas, who descended on me with true Latin hyperbole one afternoon: 'Nonono! You KEEL your parrrtner like that!' He then reverted to his (usual) Anglo Saxon mode and explained: if you bend from side to side, so that your shoulders go up and down alternately, you throw your partner off balance, as you affect her axis. (I was probably trying to lead traspie: instead I was taught to breath in slightly to lift my partner slightly onto her toes. Surprisingly, I found this takes concentration.)
But I'm inclined to think that Oscar and the local couple were both right. Oscar was talking about tango in close embrace, the local couple about tango in open embrace. In open embrace you are free to be 'expressive' with your shoulders, but if you do that in close embrace, you create problems for your partner, and she'll find you uncomfortable to dance with. Close embrace tango is incredibly smooth from the waist up, which can be very difficult to achieve. I'd watched tango for four years, but I was still taken aback the first evening I went to El Beso in BsAs to see, over the heads of people sitting down, male-female torsos gliding round, and rotating as smoothly as if they were suspended on pieces of string. Nothing I'd seen in London prepared me for that...
(I also remember a London workshop with Pablo Pugliese, who complained about what he called the 'chicken-wing-flapping' style of some dancers: in this, both shoulders go up and down together.)
Perhaps the category 'tango' contains two sub-categories, 'close' and 'not-close'. 'Close' is a specific art form involving a quality of movement that could be described as 'quasi-feline': 'not-close', on the other hand, seems pretty varied. But problems arise if one assumes that, since they are in the same category, 'tango', what goes for one is good for the other. In other words, 'close' is not necessarily 'not-close' danced close.