stem dimension make the way the bike fits highly adjustable. the short head tube means you have the option of setting it up with a super low handlebar, but it does not force the rider into that position. putting a shorter length stem on the bike will bring your hands closer to your body, which will allow the rider to sit more upright. a taller stem will have the same effect. any bike can be fitted with a shorter, taller cockpit to make it less "aggressive". a short head tube just requires more spacers and a less conventional stem to get the handlebar where you want it. there are also a few drop handlebars on the market that increase the height of the controls (Surly Truck Stop, Specialized Hover, Soma Condor, etc). so there is nothing stopping someone from setting up the Poseidon X with a upright position on a drop bar.

the top tube length on the Poseidon is not long for its size. the more you raise the handlebar, the shorter the reach gets.

take a look at the Cigne stem in the link above. that would bring your handlebar up and back quite a bit, making the fit of the bike much more relaxed and upright.