I don't understand much about mini's, so I will state that as a disclaimer. I know that mini's are registered based on height. With those under a certain height being considered mini's. I understand that back in the 80's the true mini's bloodlines were considered the fabella lines, these were the first ones in the country and were a big deal. Again, this is as I understand it and that's not very well. Some mini's are known to throw larger horses that are not considered mini's due to the heigh restriction. These horses are often selected against in many breeding programs. Its possible that your boy is considered a mini cross or is an oversized mini. I have seen a few mini's that are actually the size of small ponies.