It just seems like if you're on a mission to establish a trading route, if you arrive on an island that you believe to be off the coast of your main intended trading partner and start killing and enslaving lots of people, that might not be the most auspicious start for the impending trade negotiations.
Did they believe certain signs would be present if China were in contact with or had loose suzerain relations with some people (e.g., some sort of Great Ming flag or the like at chiefdom headquarters), and that, since the Tiano had no such signs, they must not have had any contact, and were thus fair game? Or did the they establish sufficient communications to establish that they weren't in contact prior to committing any atrocities?
I don't have an answer, but I'd like to add to the question: Did Columbus order his men to attack the natives, or did the attacks stem from a breakdown of discipline after a difficult voyage?
Columbus had no idea that the Ming dynasty was a thing, let alone how international relations worked in East Asia. His knowledge of China was so vague and outdated that he carried a letter to the Great Khan with him in the first voyage, unaware that the Yuan had been expelled from China 130 years prior.
He never assumed that the Indians he treated with were Chinese subjects for a simple reason: he asked them, and they had no idea what China or the Great Khan were. But since Columbus was delusional or a con man (probably both) he decided soon that he had hit some islands near China but not exactly China.
I'm not sure how much 'attrocities' there were in the first voyage if at all.