Like you, I have the feeling that Alec is a very busy guy right now, probably because he is writing a "How Do I Do That?" manual for the KN7000. And I suspect the holidays may have interrupted his work to some degree. He has been just super helping all of us to understand and operate our keyboards better and in the absence of any "good bye" from him, I expect him to be back soon.
I am going to take a stab at answering your question about solid state memories. I spent the bulk of my working life in electronics. While I am clearly "dated" in terms of my knowledge and experience, the fundamental principles remain pretty static. Memories are nothing more than storage areas consisting of thousands, millions, and in some cases billions of memory locations. Memory locations can be accessed by computer programs which themselves are written into memory.
In the old days of tapes, we passed a tape across a head which read the magnetized particles on the tape. The electronics inside the cassette recorder (for instance) received this information from the head, processed it, and intelligent music or speech or whatever came out of your speakers. The point here is that the head was reading the information on the tape in a sequence i.e., in simple terms - signal one, signal two and so on until the end of the tape was reached. The tape was the storage medium or "memory", if you will.
The same process can be achieved digitally. A program can be written to extract information from each individual memory location sequentially i.e., memory location one, memory location two and so on. When you play your keyboard and save the song, you are storing Bits and Bytes in memory locations that represent in digital form the sounds you played. Your sounds went into memory in a sequence over time (note after note if you will) so if our program extracts that note information from memory in the same sequence in which you played the notes, and processes the information through the electronics and eventually to your speakers, you will hear a faithful reproduction of your song.
When you push the Demo button on your keyboard, it sets in motion a computer program which interacts with memory locations, extracting sequentially what was recorded, processing the information through the keyboard electronics, which in turn feeds the results to the speakers and, voila! - music plays.
Now, after all of that, I hope I have not steered you in the wrong direction. I could go into more detail but I don't think getting more technical would be helpful to your understanding of the process. Perhaps some others would like to share their thoughts on this subject. I just wanted to keep it simple for the sake of clarity and understanding.
Hope I have helped to answer your question, Ogre. Take care.