I did not say anything about impossibilities, I said that people are good are explaining away irregularities. As this last chapter demonstrated, the students at the Academy consider Starfield to be human. Nothing has happened that would force anyone to challenge that assumption. The way Starfield dealt with Guiche may have been odd, but Starfield did nothing that could not be explained if she were a foreign mage.There's nothing impossible in their world view about some unknown human-looking magical creature getting summoned.