The angle of attack depends on the relationship between the balance point and the incidence of the stab. Increasing the angle of incidence of the stab is the same as decreasing the incidence of the wing, except that you don't affect the downthrust.
It is important to forget about the fuselage, or a datum line. What matters is the thrust line, the wing and the stab. Think of them without the fuselage. Don't be misled by the angle of anything compared to the upper longeron, or anything like that.
If a plane is nose heavy, then when you trim for level flight the stab/elevator will have to create a downward force to compensate, otherwise the plane will dive. When you put the plane into a dive, the speed increases. The increased speed has no effect on the balance point, but it DOES affect the the amount of downward force at the rear created by your trim adjustment. So when you release the stick, the increased downward force at the rear (due to your trim adjustment and the increased speed) will cause the nose to rise.
Terms like "nose heavy" and "tail heavy" can be very misleading.
Jim