Here is what Peter himself says taken from the Sonic State video interview portion around 14:45 into it.
Because I don't know much about DSP stuff.I think when he says "anyone" is a very powerful statement.
I'm just um' well, I'm just thinking about music and I'm doing my programming as good as I can.
I'm not trained in any DSP science or so because I think anyone can do it who is listening to music and looking carefully at pictures of say spectrograms or so and extracting from it.
For me there's not great mystery about that.
Reminds me of "for now we see through a glass darkly". Some things are right in front of us and there is a special type of vision or "wow" moment when it becomes clear what we are really looking at. Like everytime I go get a new eyeglass prescription ;<)
Very interesting indeed.