You ask why it is not Loshon Horah to ask about an Achsanya how hospitable he is. Perhaps we can answer in one of two ways:
1. It was an inn where one pays for service in which it is nogeah l'hefsid momon.
2. The Gemorah says that a Talmid Chacham is allowed to be Meshana Bidiburo regarding "Ushpiza" and Rashi explains because when the answer is "very good" then people would take advantage and eat him out of house and home. Of course there is no Loshon Horah in such a case, (if he says good, it is good if he says bad it is for the good of the host) Rabbi Yossi ben Asian wanted to let the person [whom he was asking about the Achsanya] know that he too was a Talmid Chochom [and therefore he asked in a manner of Chochmah] and that he would not take advantage of the Achsanya, and thus the person he was asking should tell him the truth!