It’s just a projection miss, not a massive shift. Comcast has ~32 million broadband subscribers so a decline of 18k is only ~0.06%.
I believe the article talked about Xfinity and their 5G subscriber increase as well. That is not surprising since they were doing some really shitty dark pattern stuff on their website for it. It wouldn’t surprise me if half those people didn’t even know they had signed up for it.