As a layman, I cannot give a very informed opinion, but for me, the sentence below from claim 19 in the original patent helps me to make sense of the arguments. The sole memory is referring to the "received processed sound," which has nothing to do with RAM. This seems to be the basis of the idea, "if you remove the flash memory, the device stops playing." It is not saying that the flash is the sole memory of the device, just the sole memory where the voice (or music, photos, etc.) is stored. Comments from those with more expertise?

A flash memory module which operates as sole memory of the received processed sound electrical signals and is capable of retaining recorded digital information for storage in nonvolatile form.