Wrong stamp and wrong rate; shouldn't it be 5 cents?
I think we need a postal history/rate specialist to properly answer this question. Since I am neither, I will opine.
If mailed directly to the US Military base at Columbia Barracks, I think 5 cents was the correct rate. I loaned my APO book to a friend years ago and he still has it (aaahumph, murmur...) so I can't look up to see if there was an APO there. If there was, then 5 cents would not be the correct rate (too much).https://en.wikipedia.org/wiki/The_Ansonia
I did look up the Hotel Ansonia, interesting read, and beautiful building!!!