After so much discussion of the subject, I finally broke down and wrote to “HELP.” Asked them the direct question about how these things got on the feed. Their answer, so far, has been fairly specious. Some parts I understand, because—algorithms being what they are—it’s obvious.
You read something, then anything similar to that goes into your feed “Based on your history”; something someone else you read reads something...”Based on your history”; someone you follow...”Based on your history.”
What gets me is the “Popular on Medium” which sometimes doesn’t appear to be very “popular.”