This isn't exactly the way it works, but it's a simple illustration to help you understand what this is capturing:

Let's say we play a team that in its first seven games has scored 14, 17, 13, 10, 7, 13, and 10 points, all against average defenses. And let's say that we give up 24 points to their offense. They averaged 12 points per game against average defenses, and we gave up twice that much. That 24 points we gave up isn't going to count as 24 points against our SOS-adjusted PPG; it's going to count as a lot more than 24.

Bill Connelly does something slightly different, because he goes play-by-play and looks at the expected points an offense would score from a given spot on the field. So long drives count more heavily against a defense than short drives do. That's why Toledo's TD from the 1 wouldn't hit our defensive metrics that hard; they had an extremely high probability of scoring a TD from there, so it's not a knock against our defense to give up that TD. But the example I shared should still help anyone see why we can only give up more than 30 points once and still have a SOS-adjusted PPG of 30.