Anyhow, Jeff wrote me an email a few minutes ago to sort of explain his set (and I'm glad he did):
"Hey Ryan--Thanks for the mention in your blog. I just wanted to let you know that you did actually experience Tone Ghosting. These days, all the noises from scraping vinyl LPs with hacksaws are contained on loops that I manipulate during my set. Lately, I've been making the drum machine rhythms more regular, too. It's all improvised, so I'm always changing it around. Lots of people want to see the record sawing, it seems. I may have to give the people what they want! They may be sorry!"
So yeah, there it is: Tone Ghosting.
Thanks, Jeff, for the email and for the clarification.