I feel like this is antiquated language in their TOS. It probably dates back to the introduction of broadband residential services, when the cost of delivering network bandwidth was much higher.
But they keep it there as it gives them a nice, ambiguous set of terms they can either hide behind, or use to beat you over the head for a variety of reasons.
I’m guessing they, for whatever reason, temporarily blocked incoming packets going to common ports on your service. Maybe, at some point, the underpaid, overworked network tech on night shift realised they’d inadvertently turned on/off some inbound rule when troubleshooting another customer’s problem, and changed it back.
But, you can’t complain to them about it because you can’t “hOSt a SeRVeR”. Bloody ISPs.