I think there has to be a far more intelligent design involved. The furry titan was surprised that man kind developed the gas canisters that allows the small humans movement.
Plus the big question is the involvement of a certain group of people capable reading text different than the standard language on a tin can of tuna, which I think is more technically advanced for the humans. Tuna is found in oceans, which the current humans have no exposure to.
I would have to think that Eren's dad knows of the inner workings of the world around them and has some type of knowledge on why the titans exist and how they form. How did he inoculate the humans against polio, or whatever disease that spread prior to the start of the anime? Are these people being herded to one section of the world for hundreds of years? We learn of Mikasa's past, as she is one of the few Asians descendants left... So racially these humans don't comprise the greater humanity. I see a lack of black, arab, persian, or asian people in the current (anime's) world's makeup.
Going on a limb to say that final twist in this anime will be similar to to Fractale or Scrapped Princess.