Apparently it’s “stomp” which is a very fun name for an ugly ass design. Apparently (according to a few tutorials I’ve watched since I finally found the damn name for it!) you can either sand or scrape this stuff, depending on how easily it comes off with a scraper. Some people find the scraping easier, some prefer sanding. I’m gonna try both on a sample and see what seems easier/quicker and/or nicer finish for my ceilings, and will go with whichever I think might work best. Thanks for your help!