If you understood my previous posts, you'd see that I meant that they are using developmental standards that apply to the whole population. If I tested a six-year-old with osteoporosis and conclude that the bone density is like that of an 80 year old woman, do I conclude that the six-year-old is an 80 year old woman? No, because she has osteoporosis and so my test is not relevant. It's kind of similar to how athletes can't have their health determined by their BMI. It doesn't appear to hard to measure bone density anyways - all you have to use is medical imaging technology like MRI's or CT's.
And while it's unlikely, it's plausible. You're conflating the two ideas - of course genetic disorders or mutations are unlikely or else we'd all have them! - but it's still a plausible explanation because you're using the known to explain the known and hopefully come to some conclusion about the unknown. If you're going for an alien DNA thesis then you're assuming the unknown, which doesn't explain what's known so how can you come to a reasonable conclusion about what you don't know? Alien theories aren't plausible to begin with - but we know mutations cause deformities. That's all I think I need to say about the strength of the earthly human argument.
I wouldn't say my theories are untestable in general - just that in this particular situation it might be difficult. Before we even go there, the researchers - and I as well - agree that the specimen is human. The anatomy and the genetics scream human. Context include mtDNA of a Chilean, anatomy of a human body, DNA "closer to humans than chimpanzees". That's scientist talk for "my years of experience and expertise say it's human, but I'm still a scientist so I can't say 100% unless I've ruled everything else out". They are testing for mutations right now, and hopefully they'll come up with some data useable enough to flesh out how the morphology of the specimen can be explained.
91% of the DNA correspond to a reference genome. The 9% that doesn't is in acceptable errors and doesn't mean anything out of the ordinary. This is firmly in a scientific context, so it's not up to anybody's whim to say "well, 9% seems like a lot, I guess I'll conclude it's not human". Inaccuracy, DNA degradation, or not actually having a match in the genetic database are all possible and expected. That's why they're going to do more reads on more genetic databases, preferably those taken from Chileans or at least related populations to come up with more matches. This is the report from which I'm getting this information:
The body most certainly went through some damage before we found it, otherwise the skull would be still attached to the spine where it should. I posted this two posts before, but I guess details aren't important...
Edit: Here's a wiki page that explains my previous post if you don't believe me: