If you had sent it signed for it wouldnt have made a difference, a signature is rarely readable and people sign just X. As others have said you cannot loose as you have delivery confirmation to the given address. It is his mistake but I understand your feeling of perhaps you could have cancelled and the guy re order with another address. But I also see it could have been a scam, He may have the parcel from the other address as they could be friends.
Its a difficult one if you are an honest good person and take things to heart but you haven’t done wrong. You could of genuinely packaged and shipped within say 15 mins of the order if you were packing other orders and you would be in the same position.
I have my suspicions when people loose their temper when its genuinely their fault. If they said terribly sorry I’ve made a massive mistake and sent it to my old address then I may think differently.