That's sad that you couldn't get a decent explanation.

You might try emailing exactly this writeup to feedback@amazon.com, including the URL to your brother's wish list and which item you were trying to buy. (I don't remember whether that's the address for feedback where you do want a response or feedback where you don't care whether you get an individual response or not, but would like Amzaon to know so they can try to fix the problem.)

My guess is it has to do with privacy issues around your brother's wishlist's ship-to address and items sold by non-Amazon merchants.