This is half Amazon's problem, and half Apple's problem for not giving their computer models unique names. Type iPhone 6s and you get much more clear results.
No, it's that these listings on Amazon are kind-of-like "eBay" just without the auctioning part. The seller can write whatever he wants. Amazon just evaluates the complaints of the buyers.
There is a standard naming convention with Apple products though that they and everyone else uses: