I don't think the CGI has the stack arrangement correct. I think the CGI simply follows the land mockup. But I think the land mockup omitted the upper parts of the stack. The reason is I am not sure having stacks as low as commonly depicted for type 055 is tenable. I assume the ship will be gas turbine powered and will have facility to entrain embient air into the exhaust gas before emitting the exhaust gas into the atmosphere in order to reduce IR signature. This suggest the exhaust will emerge at relative low pressure and velocity. Which means the exhaust can be blown about by ambient wind before it travels very far up. This in turn suggest having stack so low as depicted in the CGI and so close to the radar mast means the radar masts may be subject the heat and corrosion by the exhaust gas.
So I think the this will have stacks of normal height.
I don't think the exhaust structure on the mock up is at an unnaturally short height -- I think it just seems that way because the integrated mast adds a bit of additional height to the overall bridge/superstructure of the ship, making it seem like the exhaust level of the mock up may be a bit too low and cause exhaust to be "closer" to the mast.
However, this isn't actually that rare, for example the 054A's surface search radar/Type 346 is located right on top of its exhaust and often becomes covered brown due to its proximity to the exhaust, and if one looks at the mast the Type 346 sits on it is painted black so that the exhaust corrosion/discolouration is less obvious.
It is even more obvious on the Type 45, which has not only the SMART-L in close proximity to its aft exhaust but also the main forward mast which is rather tall close to its amidships exhaust, causing the rear side of both masts to be painted black in a rather not subtle way to avoid the discolouration caused by the exhaust., along with the ESM mast in the middle which of course is directly behind the path of the amidships exhaust.
So I think the height of the 055's mock up exhaust is not necessarily unrealistic. It may end up being different on the real ship, but I don't think the idea of the exhaust level interfering with the mast is necessarily a reason to think that as other ships have shown it's not that big of a deal to have the exhaust in relatively close proximity and height to a mast.