Yeah, Spreaker can do that; it's weird. If I set that "Manage RSS" option to "enabled" (which is the default), it will publish a Spreaker-hosted RSS feed with added elements, kind of like Feedburner's old SmartCast feature worked.
In fact, do you remember a couple of years ago that my own podcast was duplicated in the Index? We traced that to the scraped Spreaker RSS feed that I didn't realize was being created by Spreaker.