My main takeaway from Demoscene is not "compression"
Compression is still a big part of it, just not in the "take the original data, minimize it and reproduce it later" sense of the word. The procedural generation employed by these demos is still a form of compression: the highly-specialized decompressor needs only a few bytes of information to create the intended effect (texture or shape).
If anything, it shows how much compression can be achieved if the decompressor can be tuned to the data domain, as opposed to general-purpose compression algorithms.
It is not just a matter of information science in terms of "how can one concisely describe the object - that would be the strict informational content", but also clever procedural method to generate an output starting from the specifications of a machine.
In the case of flt's "A mind is born", several efficiency techniques are used - overlapping of palette and SID registers etc., but especially notable could be that the melody is generated by a sequence-after-seed process (Linear-Feedback Shift Register), where the seed is chosen so that a good melody is returned ( full explanation of the code: https://linusakesson.net/scene/a-mind-is-born/ )
Compression is still a big part of it, just not in the "take the original data, minimize it and reproduce it later" sense of the word. The procedural generation employed by these demos is still a form of compression: the highly-specialized decompressor needs only a few bytes of information to create the intended effect (texture or shape).
If anything, it shows how much compression can be achieved if the decompressor can be tuned to the data domain, as opposed to general-purpose compression algorithms.