Not necessary.
@by78 posted an research paper in
#97
The paper showed an illustration of a sub with the reactor compartment being in the middle just behind the sail. If this illustration mean anything serious, the reactor can be the cause of a hump.
It is only the reactor pressure vessel and maybe the first loop in this section, the second loop, steam turbine and drive (electrical or gearboxed mechanical) can be placed further aft. The pipe between the first and second loop can be placed through the opening between the middle and aft pressure hull.
The paper was published in 2009. The simulation tests must have been concluded by then. So there is 10 years to do some water-tank tests before building a full-sized sub. BTW, multiple pressure hull construction is not new idea as Project 941 has done that decades ago and proven to work well. It would not have been an extreme challenge for China to do so in a much smaller size many decades later.
I won't say for sure that the hump is due to a new reactor, but it is a good possibility.