By Archimedes this equation is true only if the density of the transported goods is 1000 kg/cubic meter or smaller.There can be no doubt this hull is a warship. The clinching factor isn’t the size of the supposed engineering space or how it is being assembled. There can be a number of reasons why the Chinese choose to build the engineering space the way they’ve done. The clinching factor is the side wall of the hull is so thick (around 7 meters) it must contain a fairly deep underwater protection system. No merchant double hull is going to consume 7 meters of otherwise revenue making Space. No merchant ship would need such deep compartments on either side of the central hull cavity.
For example if the ship designed for iron ore (density 2.5kg/liter) then at least 60% of the average ship cross section must be air.
Considering that the material of machines is usually iron, and they are quite dense ,this big ,uninterrupted space still doesn't make sense for a warship, unless it is just a step in the construction process.