This part is unquestionably true. But since we don't have a direct measurement of the stored energy at a given time, the occurrence of an earthquake acts as both an indicator of release of stored energy but also, potentially, evidence of increasing stored energy.
Like how buying a Porsche costs money, and leaves you poorer than before you bought it, but when you see stranger buy a Porsche, you update towards believing that they're wealthy rather than poor.
Disclaimer: I am not a geoscientist.
Fair enough. I'm also not a geoscientist, and to clarify I didn't mean to imply any specific statistical effect there. It seems entirely reasonable to me that a series of EQs might tend to increase in intensity.
In reality I think (layman's impression) that there's rough (post hoc) evidence for both things. Foreshocks followed by noticably larger EQs as well as trains of progressively smaller EQs.