The effect of seeing a program run in visible video RAM was actually pretty common on the C64.
Memory was really tight and every byte was valuable. Also external memory was slow. Programs were often loaded in a compressed form and then uncompressed. Since the uncompressed version filled the available memory to the last byte it raised the question where to put the unpackers code.
A natural choice was to run it from video ram, which would be overwritten when the game started and the unpacker was not needed anymore. As slow as the C64 was, you could clearly identify the unpackers loop counters.
I have also heard the story that this trick was especially popular for pirated games. The crackers used to add their intros and they had to fit in somewhere into already filled to the brim memory. So they used compression to squeeze their intros in.
Memory was really tight and every byte was valuable. Also external memory was slow. Programs were often loaded in a compressed form and then uncompressed. Since the uncompressed version filled the available memory to the last byte it raised the question where to put the unpackers code.
A natural choice was to run it from video ram, which would be overwritten when the game started and the unpacker was not needed anymore. As slow as the C64 was, you could clearly identify the unpackers loop counters.
I have also heard the story that this trick was especially popular for pirated games. The crackers used to add their intros and they had to fit in somewhere into already filled to the brim memory. So they used compression to squeeze their intros in.