I emailed a breeder who has some large Chihuahua's, along with the smaller ones. One of her females is 12 pounds
I wrote her and told how much he weighs (almost 6lbs) his age, and 3 pictures. I got a reply within 45 mins. This is what she sent
"What most people don't understand is that there are many varations in chihuahuas. Bambia, my 12 pounder is a deer head. Their head is a bit more flat and their nose is longer than their show counterparts, in no way does this make then a less better pet. I would say that Zeus is a pet quality chi that will probably get about 10-12 pounds, and he is a cutie! Either his parents were larger, or even his grandparents, sometimes it can hide a generations."
I wrote her back asking if Zeus is an apple head or a deer head, she replied this morning and said he looks like a deer head, guess we'll see as he gets bigger
Just thought I would share that since I was questioning him being pure as well.